Keep Pebble connected at all times - #12

As usual, check commit messages for detailed list. Remarks:

• After this PR, there is an extra pairing step. After user selects the watch, he/she must confirm to connect to the watch via Android system dialog. This is required for us to use Android's CompanionDeviceManager which has quite a few benefits (for example much more user-friendly flow for enabling notification listener service). We might need to adjust designs to accommodate this
• I've moved logging to Timber. App now creates logfile in data folder and there is a button on the Testing screen that allows you to share logs out of the app. This will allow us to test app in the wild without being tethered to the PC to constantly observe logs. Log sharing code should eventually be moved to flutter, but I do not know enough about Flutter, so I whipped it up it in native Kotlin for now.