[ENH] Dark light theme

[rksh]

massive refactor to allow the app to respect Android's day/night theme support.

• "Day" Currently disabled pending extensive testing
• extensive replacement of bitmaps with vector assets
• fixes for assumptions/incompatibilities
• menu item visual cleanup; retirement of exit row background color (since android NavDrawer doesn't allow it)
• implies but does not yet use a SharedPreferences entry to switch themes
• centralizes theme to application rather than asserting per activity
• tons of lint-ing
• removal of harcoded colors
• fixes for vector-to-image in pre-M android version