[EGD-4852] Add sleep mode for GSM modem

When the GSM modem is idle and there is no communication,
it enters the sleep mode, where the power consumption
is significantly reduced.

[EGD-6308] Add block CPU frequency decreasing for connected USB

While the USB cable is connected, the battery charging works,
so in this case energy saving is not critical
and for a more stable transmission, we block decreasing
the CPU frequency below 132 MHz.

[EGD-6280] Further changes to Pure menu wording

Fixed 'Advanced' title.

[EGD-6280] Further changes to Pure menu wording

Fixed 'Advanced' title.

[EGD-6263] Add  automatic linear brightness

Linear automatic backlight controller - part1

[EGD-6105] Fix database synchronization

std::fflush used in the sqlite3vfs sync only the stdio buffer
but without sync internal filesystem. Additional fsync call fix
this issue.

[EGD-6052] Add idle BT device disconnect

After 30 minutes of inactivity (no stream) the device
is disconnected

[EGD-6280] Further changes to Pure menu wording

Added small fixes to the wording before sending phones to testers

[EGD-6288] Fix torch turnoff

Fix of torch behavior on close
system event. It will be turned
immediately on shutdown request.

[EGD-6168] Lock CPU frequency only while BT is working

Due to fixed BT transmission, the CPU frequency can be lower.
To be more power-friendly, minimal working freq is being set while
working with Bluetooth

[EGD-6259] Turn off usb security

To prevent errors with USB connectivity and charging screens.

[EGD-5744] Phone mode status bar widget

Added phone mode widget to top bar. The widget is mutually exclusive
with NAT widget. Phone mode is determined using phone mode observer.

[EGD-6455] Fix modem AT command timeouts

Fix modem AT command timeouts and make sure they are at least
bigger than the ones defined in Quectel specs.

[EGD-6455] Disable service audio debug loggs

They were too much of them

[EGD-6455] Fix for incomming text messages issue

There was no proper error handling.
Minor routine refactor

[EGD-6264] About Your Pure Main Window

Add window About Your Pure to help display Technical Information,
Certification and SAR.

[EGD-5783] Revert EGD-5783

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

[EGD-6282] Add marketing-friendly test messages to Pure

Added a long 4K note from a book and Mudita-related.

[EGD-6282] Add marketing-friendly notes

Added a marketing-friendly notes and a 4K chars passage
from 'The Picture of Dorian Grey'.

[EGD-6277] Changed contacts to English names

Changed contact names and contact details to 
more marketing-friendly.