Fix MarkedSeekBar positioning, tweak styling.
[FIXUP] Unused imports and variables.
Fix most of app bar / action mode styling.
Fix crash when toggling playback, clean up.

On Android 5 the activity crashes due to ContextThemeWrapper hiding the
methods used by OnClickListeners in the XML.
Temporary fix for crash from empty annotations.
[FIXUP] Remove tests that I forgot about.
Lay groundwork for an event based architecture.
Refactor video grid and tabs, restyle items.

Now adheres more closely to the material design guidelines.
Merge branch 'improvement/LL-831' into review

Conflicts:
	app/src/main/java/fi/aalto/legroup/achso/activity/MainActivity.java
	app/src/main/java/fi/aalto/legroup/achso/activity/VideoPlayerActivity.java
	app/src/main/java/fi/aalto/legroup/achso/fragment/VideoBrowserFragment.java
	app/src/main/java/fi/aalto/legroup/achso/util/App.java
	app/src/main/res/layout/partial_playback_controls.xml