SleepTimer

SleepTimer is a timer, like the ones in TVs an Hifi systems. After a specified time the devices
standby mode is activated, as if the power button was shortly touched. It doesn't matter if a video
or audio stream is played or another app tries to prevent the standby mode.
Reactivating is possible by a short press of the power button.

Features:
- permanent notification showing the remaining time until standby
- possibility to use Androids quick settings for pausing and resuming a countdown

fixed:
- no notification on android 13+
- click on notification started new app instance, after leaving app with device "back" button, instead of "home" button
- code refactoring: removed non english source code elements

added:
- set min Android Version to 7
- set max Android Version to 15
- updated dependencies