[BH-1765] Added missing python requirement

while setting up MuditaOS toolchain in a virtual environment
I noticed a requirement was missing. Probably it comes preinstalled
on Ubuntu so no one noticed until now.

[CP-2184] Fix Pure not connecting to MC after leaving tethering

Fix of the issue that after disconnecting tethering Pure
would not connect back to Center, only USB cable
reconnection would resolve the issue.

[MOS-1036] Fix song time not updated when returning from list

* Fix of the issue that switching from songs
list to main view after playing and stopping
some track resulted in elapsed time counter
not being updated until the song is unpaused;
* cleanups.

[MOS-948] Fix for tethering popup was losing user unsaved data

Fixed data loss when creating or editing a note/contact after connecting
the USB cable and selecting the option to enable tetering in the popup window
that appears. Now, when the user wants to enable tethering, they will be asked
if they want to exit without saving.

[MOS-1011] Fix frequency switching stability

Multiple fixes of clock switching related
stability issues:
* added RC oscillator hysteresis as in NXP example;
* changed DCDC converter config;
* configure PLL2 to be able to run on any CPU
frequency level;
* added switching to 1.275V (overdrive) voltage
when applying any clock change above 12MHz as
well as LDO or bandgap switching, as done in
Mbed OS' lpm.c for RT1050;
* changed BMCR AXI queues weighs for SDRAM
in JLink scripts to disable operations
reordering, as it is known to cause data
integrity issues;
* extracted some code to separate files;
* smaller or bigger code cleanups.

[MOS-1032] Fix misleading 'Save' button behavior when setting time

Fix of the issue that pressing 'Save' when setting
time would set the time indeed, but the UI would
not return to previous window, what might look
as if saving failed.

[MOS-1030] Fix for losing drafted message and recipient number in new message windows

Fixed a scenario where a user left a draft message with the recipient's phone number
in the new message window, and when they wanted to go back to that message,
the phone number and message could disappear.

[MOS-1007] Fix for no popup when contact cannot be saved because of same nubers

Fix for fix. It add popup when user try to save contact witch practically
the same numners  (even if having a country code is only difference)

[MOS-552] Fix alarm clock input behavior

Fix of multiple issues that manifested in
input fields of alarm clock, i.e. value
not erasing automatically, redundant
double-zero filling of hours field,
lack of zero-filling of minutes field
when navigating to AM/PM field in
12h mode.

[MOS-1031] Fix Meditation app screen lock

Fix of the issue that Meditation app
would prevent phone from locking on
every screen, though it should do
so only on timer screen.

[BH-1720] Changed misc-tools to point to current master

After some previous commits to misc-tools, the MuditaOS misc-tools
submodule version was not updated. Now the version in the MuditaOS
repository will be up to date.

[BH-000] Update changelog

Create section for 2.1.0 version in the changelog

[MOS-1020] Fix for losing unsaved data

Fix for losing unsaved data when the user click the BACK button while
creating or editing note/contact.

[MOS-1028] Fix corner case with input mode in Notes app

Fix of minor corner case bug in previous
implementation - pressing left functional
button when selecting input mode would
display empty options menu even if note
and clipboard were empty.
Additionally fixed the same bug for
'Save' button.

[BH-1761] Add a log when manual reset is performed

If the user performs a manual reset there is no information in
the logs. It can be treated as software resets.
So the best solution is to add a log about incoming
manual reset and dump all logs to the file.

[MOS-1029] Fix missing 'Copy' option on 'New message' window

Fix of the issue that copy to clipboard option
was missing from the menu on 'New message' window.

[MOS-1028] Fix possibility to copy text from empty note

Fix of the issue that in Notes app 'Copy text'
option was shown in 'Options' menu even if
the note didn't contain any text.

[MOS-948] Revert: Fix for tethering popup was losing app context

Reverting previous fix because when tethering is switched on the user
are not able to use phone features, and we this fix make the user
to pass this block and it would make their confuse.

[MOS-1027] Fix lack of tethering icon on 'Tethering is on' popup

Fix of the issue that pressing menu button while
in tethering resulted in LTE and no signal icons
appear on status bar instead of tethering icon.

[MOS-1021] Fix blocked passcode behavior

Fix of the issue that after blocking
passcode from Center, Pure would still
display passcode input popup; providing
valid passcode there would result in
phone entering invalid state, where it
behaved as if it was unlocked, but
with blocked passcode.