[CP-206] Report Pure serial number in USB descriptors

Added serial number to USB device descriptor

[CP-143] Set 204 code for responses with empty body

Body field was always added to response json, even if
it was containing only null. Now empty body is
not attached to response json, and status code
for such message is set to 204. Additionaly some
minor cleanup in service desktop was done.

Merge branch 'master' into stable

[BH-373] Convert utils json into a lib

Moving json to a third-party standalone library.

[BH-378] Utils move log to library

Moved log to separate library

[CP-84] Implement Security API

- Added pass code unlock from MC
- Removed Set USB security status
- Changed isLocked to phoneLocked in request for phone lock status
- Removed remainings of USB security in Settings App
- Reworked USB security model to depend both on
    Phone lock state and Pass code being enabled
- Updated test_security.py

Merge branch 'master' into stable

[EGD-6701] System time usage fixes

Fixed all calls to stdlib time.
Removed all redundant calls to Timestamp treated as time source.

[CP-120] Fixed USB comm. when Pure reconnected unlocked

USB comm. was secured when Pure was reconnected to PC while unlocked

[CP-2] I don't want to see data from Pure in Center when Pure is locked

[CP-48] Re-enabled USB security
[CP-49] Update test harness with usb security

[EGD-6019] Minimum settings ownership lifetime fixups

added weakptr link to settings and checks
    it wont crash on deinitialized setings now
Pseuto UT are passing
Added:
    - deregistration on Settings destrution
    - weak referencing of Service to not crash Settings on missuse
    - Proxy as initialization parameter to Settings
Unused code removed
Enabled tests to be written for Settings
Removed dependency from freertos in test global file
EntryPath tests updated and compilation slimed

[EGD-6019] Revert of two commits

This reverts commit b6416b15dac3a638d803681fbad8746b1808b6aa.
This reverts commit e2f3882d8a0194ae6f74bfc5ab6104c368174517.

[EGD-6019] Minimum settings ownership lifetime fixups

added weakptr link to settings and checks
    it wont crash on deinitialized setings now
Pseuto UT are passing
Added:
    - deregistration on Settings destrution
    - weak referencing of Service to not crash Settings on missuse
    - Proxy as initialization parameter to Settings
Unused code removed
Enabled tests to be written for Settings

[EGD-6729] ServiceDesktop plug off lock interactions fix

ServiceDesktop plug off lock interactions fix.

[EGD-6676] PhoneLock handling with ServiceDesktop

Replaced old PhoneLock handler in ServiceDesktop with new
interactions with Application Manager PhoneLockHandler.

[EGD-6615] Fix tethering repeated notification

Repair of repeated tethering notification
after disconnection.

[EGD-6209] Tethering confirmation popup added

Provided a tethering confirmation popup.
The popup shows up once a USB cable is connected to a PC.

[EGD-5834] Fix restore API

Change restore API
backup/restore/update harness tests

[EGD-6259] Turn off usb security

To prevent errors with USB connectivity and charging screens.

[EGD-5783] Revert EGD-5783

Revert "EGD-5783 Exclude empty body from response message"
This reverts commit b64eb0622b6c5e59eeb2161223e793ba4164ceb9.