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)
-Previous version used emojis for brightness and volume icons, which may
be inconsistent across devices and do not fit well with other parts of UI
(Frankly, previous version was more informative than eye-candy)
-This commit replaces old version with circular progress bar that shows
current value (before conversion). Gesture mode (volume/brightness) is
indicated by icon that changes between (4/3) modes according to current
value
-Text information about current value was removed, because with progress
bar present it does not add any real value to UI.
