For all manually-created images PNG have been kept.
- rename all icon attrs to have a `ic_` prefix
- always use `_24dp` icons, because there is no real difference, since they are vector drawables
- always use the original name found on material.io for icon drawables, as to not create confusion and possibly duplicates. Icon names can still be different from real drawable names, though I have made some of them compliant to this or maybe more meaningul.
- remove duplicate `getIconByAttr()` in ThemeHelper (use `resolveResourceIdFromAttr()`
- use standard icons for `expand_more` and `expand_less` instead of triangles
- use `play_button_outline` instead of custom PNG as play button in VideoDetailFragment (questionable, as there is no shadow anymore)
-Added previous and next button on main video player.
-Reverted double tap to seek for popup and main video players.
-Improved shuffling to use recovery record.
-Changed shuffling to place current playing stream to top of queue.
-Fixed exception when removing last item on queue.
-Changed fast forward and rewind button to previous and next on background notification.
-Changed background notification to not update when screen is off and update immediately when screen is turned back on.
-Removed unused intent strings.
-Changed "Append" to "Enqueue" for append text.
