WARNING: This version is probably a bugfest, just like the last one. However, due to the complete shutdown of the application since the 17th, a faulty version is better than no version at all. Isn't it? ¯\_(ツ)_/¯

### Improvements
* downloaded files can now be opened with a single click #1879
* support for Android 4.1 - 4.3 removed #1884
* remove old player #1884
* remove streams from current play queue by dragging to the right #1915
* remove automatically queued stream when a new stream is manually queued #1878
* Post-processing for downloads and implementation of missing features #1759 by @kapodamy
  * Post-processing infrastructure
  * Error handling infrastructure (for the uploader)
  * Queuing instead of multiple downloads
  * Move serialised pending downloads (`.giga` files) to application data
  * Implement maximum repetition of downloads
  * Pause multi-threaded downloads
  * Stop downloads when switching to the mobile network (never works, see 2nd point)
  * Save the number of threads for future downloads
  * Many inconsistencies corrected

#### Fixed
* Fixed crash when default resolution is best and mobile data resolution is limited #1835
* Fixed pop-up player crash #1874
* Fixed NPE when opening a player in background #1901
* Fixed insertion of new streams when auto-queuing is enabled #1878
* Fixed shuttown decoding problem