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)
-Fixed bookmark button flickering on visibility toggling.
-Removed toolbar up button control from local fragments, delegating functionality back to main fragment.
-Updated extractor to latest.
-Added LeakCanary as part of debug build.
-Modified bookmark list to show both remote and local playlists.
-Removed ability to save channel items as local playlist, in favor of subscribe.
-Added playlist append menu item to channel and playlist fragments.
-Added debouncing to local playlist fragment to allow saving join when list is reordered or item is deleted.
-Extracted hardcoded strings.
