[EGD-6111] Timers refactored

Deep refactor of system timers.

[EGD-5658] Add eInk CPU frequency hold

While the screen is being redrawn,
we block CPU frequency decreasing

[EGD-4853] Add Wake up GSM modem on demand

System wakes up Cellular when there is a need to communicate
with the modem, e.g. to handle an outgoing call

[EGD-5969] Add battery charging UI

Battery charging UI modified
according to design

[EGD-5918] The system should crash on init failure

ServiceDB init process times out. Its timeout should be extended.

[EGD-5304] Add new way of system close

Unified method of closing
the system orchestrated by
system manager

[EGD-5771] Create post update info window

Add post update info window.

[EGD-5756] Add Update Window

Create Update Window(s) to control and visualize the MuditaOS update
process on Pure.

[EGD-5836] Turn on/off the tethering via harness

This allows a user to turn on and off the tethering via test harness.

[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 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-5697] Framework for phone modes introduced

It allows to transmit phone modes information to listening services.

[EGD-5324] Add Low Power documentation

Documentation describing the Low Power control algorithm and
synchronization with the system using dedicated sentinels and drivers.

[EGD-4797] Battery bar as widget

Battery bar now is present as
a separate widget in top bar.
Additionally refactored passing
battery status.

[EGD-5382] Add LowPower CpuSentinels

In order to synchronize the Low Power mode, the services were
immediately informed about the frequency change,
so that they can update their resources (e.g. PWM filling)
and services may request the maximum CPU frequency in order
to perform a task (e.g. screen redraw, telephone conversation)

[EGD-4068] Add Update Package Installation Mode

It is necessary that the PureOS update mechanism enters Update Package
Installation Mode (where most of the services are stopped)
when the PureOS update package gets downloaded into the phone.

[EGD-5027] Services synchronization introduced

Dependencies between services are now supported.