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)
Post-processing infrastructure
* remove interfaces with one implementation
* fix download resources with unknow length
* marquee style for ProgressDrawable
* "view details" option in mission context menu
* notification for finished downloads
* postprocessing infrastructure: sub-missions, circular file, layers for layers of abstractions for Java IO streams
* Mp4 muxing (only DASH brand)
* WebM muxing
* Captions downloading
* alert dialog for overwrite existing downloads finished or not.
Misc changes
* delete SQLiteDownloadDataSource.java
* delete DownloadMissionSQLiteHelper.java
* implement Localization from #114
Misc fixes (this branch)
* restore old mission listeners variables. Prevents registered listeners get de-referenced on low-end devices
* DownloadManagerService.checkForRunningMission() now return false if the mission has a error.
* use Intent.FLAG_ACTIVITY_NEW_TASK when launching an activity from gigaget threads (apparently it is required in old versions of android)
More changes
* proper error handling "infrastructure"
* queue instead of multiple downloads
* move serialized pending downloads (.giga files) to app data
* stop downloads when swicthing to mobile network (never works, see 2nd point)
* save the thread count for next downloads
* a lot of incoherences fixed
* delete DownloadManagerTest.java (too many changes to keep this file updated)
