[EGD-5783] Exclude empty body from response message

Remove body field from response message,
if it contains null. Add 204 and 501 status codes
and use them in proper responses.
204 stands for success but no content, and 501
means endpoint is not implemented.
Additionally some minor fixes.

[EGD-6191] Fix harness call tests

* This PR provides a fix for the bug reported in [EGD-6081].
The solution adds the `tear_down`-like fixture called after the
problematic tests, that enforce focus on `ApplicationDesktop'`s
main window.
* Additionally similar solution was added to `test_auto_lock`
to restore original (30s) lock timeout.

[EGD-6081]: https://appnroll.atlassian.net/browse/EGD-6081

[EGD-6232] Fix Harness does not unlock endpoint

USB unlocked in tests
Adjustment of tests to the new EP API

[EGD-6230] Fix reading of cheksum.txt file

Fix errors regarding update.

[EGD-5945] Bluetooth-harness API messages

This PR:
* provides Bluetooth-Harness API messages definition [EGD-5944]
* provides Bluetooth-Harness API messages implementation
* provides Bluetooth-Harness API usage on harness side [EGD-5946]
* provides Bluetooth-Harness tests [EGD-5947]

[EGD-6076] Fix test_send_message  fails

fix for function erase_all_templates

[EGD-6196] Replace venv command in harness readme

Replaced to avoid usage of python2

[EGD-5965] Add BT-Harness API documentation

Added documentation:
* BT endpoint API
* BT-Harness tests

[EGD-5565] Fix update process on new lf filesystem

These changes are needed for update to work with new
LFS fileystem, also minor bugfixes are included.

[EGD-6100] Add BT device turn off handling

After BT device disconnects (e.g. because of shutdown) Pure is now
aware of this

[EGD-5512] Usb security refactor and devices pairing

Move all security related functionality to single security endpoint
Paired devices can be added to avoid further passcode requests

[EGD-6106] Fix update test on CI

Update test is marked as rt1051 so CI ignores
it during testing

[EGD-6022] Fix tests used in CI process

Fixed some tests used in CI

[EGD-6027] Moved test harness to separate repository

Common code for QAE and development moved to separate repository to
achieve more granular controll and more fluent flow

[EGD-5908] Fix bug in Logger + add log unit test

Because `vsnprintf` return value means:
"
The number of characters that would have been
written if n had been sufficiently large,
not counting the terminating null character.
If an encoding error occurs, a negative number is returned.
"

`Logger` crashed when log msg was longer than LOGGER_BUFFER_SIZE.
Checking `vsnprintf` return value solves this issue.

[EGD-5724] Add pagination for Templates

Add pagination for Templates
Fix bug in change message template response

[EGD-5758] Restore auto locking timer in ApplicationManager

Restore auto-locking functionality

[EGD-5906] Fix test_calendar_events

Unlock usb and enable test on CI

[EGD-5326] Fixed AT commands harness utility

We can now use test harness to send and check at commands

[EGD-5326] Fixed system messages logging crash

with messages debug utility and error on memory there  was crash