Dark Theme Fixes

See merge request briar/briar!844

Factor out keyagreement ui theme

See merge request briar/briar!835

Upgrade Android Gradle Plugin to 3.1.3

See merge request briar/briar!842

Implement Dark Theme (DayNight with automatic option)

See merge request akwizgran/briar!818

This is just a first rough implementation.
A real UI designer should look over this.

Language improvements

See merge request akwizgran/briar!829

Resolve ""Decrypting database" label needs some padding"

Closes #1297

See merge request akwizgran/briar!830

Use project path for translation verification

See merge request akwizgran/briar!840

Add utility method for logging exceptions

See merge request akwizgran/briar!838

Don't hide UI on low memory if we're in the foreground

See merge request akwizgran/briar!839

Replace logging boilerplate with a static method

See merge request akwizgran/briar!837

Move logging of time measurements to FINE level

See merge request akwizgran/briar!836

Don't show Huawei protected apps button on API 24+

Closes #1291

See merge request akwizgran/briar!823

Use placeholder text for text fields and add show password button

Closes #1096 and #1288

See merge request akwizgran/briar!834

Closes #1096

Closes #1288

Use separate strings for introduction menu item and button

Closes #1316

See merge request akwizgran/briar!833