Fixed issue on Android - wasn't able to see incoming call when phone is locked \ app in background.

[AlexBacich]

Android fixes:

• While app is in background - popup wasn't showing at all. Fixed that.
• While phone was locked - popup also didn't appear
• Noticed that there is no need to programmatically detect whether app is in background or the screen is locked. The notification popup handles both scenarios. So removed unnecessary code.

Now things are working for Android.

[Alezhka]

Thank you, but your PR touches too many different aspects of the code:
2. When app in background - popup didn't be to appear! Instead show call activity.
3. I think add variable for enable state is too much. Now ringtone enabled is not null.
4. I think use logger for production is not a good idea. Maybe need log level option for log printing. Need more think about it.
5. Too much code formatting and add/remove some spaces. (changes that do not affect the work of the code)