[EGD-5737] Merge master into experimental

Keep experimental up to date with changes from master

[EGD-5737] Merge master into experimental

Keep experimental up to date with changes from master

[EGD-5737] Merge master into experimental

Keep experimental up to date with changes from master

[EGD-5737] Merge with master

Keep experimental up to date with changes from master

[EGD-4850] Fix of statics between USB CDC and ServiceDesktop

Handling queues with static std::string implementation caused
problem of double-free memory on turning off simulator. Applied
solution to the problem is to pass ownership of queued string to
a receiver side.

[EGD-5346] Refactor of battery charger BSP

Pure refactoring of battery charger to privide compliance
 with modern C++ standards. Done before implementation of
battery charging algorithms.

Merge branch 'master' into stable

[EGD-5086] Fix voice not starting when calling

Due to a race condition between source and sink voice is not always
starting when calling. Introduce audio stream connections to avoid
race condition and improve handling of audio start and stop operations.

Signed-off-by: Marcin Smoczyński <smoczynski.marcin@gmail.com>

[EGD-4887] Add PLL2 clock switching

Pll2 will be disabled at the lowest CPU frequency,
which will save power

[EGD-4881] Add oscillator clock switching mechanisms

Osc will change automatically at the lowest CPU frequency,
which will save power

[EGD-5050] Add brownout detection

Brownout detectection realized through charger driver

[EGD-5089] linux battery bsp charging done added

[EGD-4999] fix charger pluging but no icon on Linux

[EGD-5004] Add USB-CDC echo mechanism

Added echo mechanism to USB-CDC, update usb_stack submodule
and added a test case to test harness

[EGD-4694] Add CPU frequency shift mechanism

The CPU frequency changes automatically which saves energy

[EGD-4952] Added stetings for battery critical level

[EGD-4952] Cleanup

[EGD-4952] Moved battery level check to separate module

[EGD-4952] Fixes for rt1051

[EGD-4952] Added battery check at init and if crit level changed