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)
Changed android.R.string.ok, which is "OK", into R.string.finish, which is also OK, but from our strings
Then for a small amount of languages that don't have Android translation, it will show the good string.
* migrate few annotations to androidx
* mission recovery: better error handling (except StreamExtractor.getErrorMessage() method always returns an error)
* post-processing: more detailed progress
[file specific changes]
DownloadMission.java
* remove redundant/boilerplate code (again)
* make few variables volatile
* better file "length" approximation
* use "done" variable to count the amount of bytes downloaded (simplify percent calc in UI code)
Postprocessing.java
* if case of error use "ERROR_POSTPROCESSING" instead of "ERROR_UNKNOWN_EXCEPTION"
* simplify source stream init
DownloadManager.java
* move all "service message sending" code to DownloadMission
* remove not implemented method "notifyUserPendingDownloads()" also his unused strings
DownloadManagerService.java
* use START_STICKY instead of START_NOT_STICKY
* simplify addMissionEventListener()/removeMissionEventListener() methods (always are called from the main thread)
Deleter.java
* better method definition
MissionAdapter.java
* better method definition
* code cleanup
* the UI is now refreshed every 750ms
* simplify download progress calculation
* indicates if the download is actually recovering
* smooth download speed measure
* show estimated remain time
MainFragment.java:
* check if viewPager is null (issued by "Apply changes" feature of Android Studio)
