Revert ExoPlayer to 2.15.1

Apply track selection fixes

Backport track selection fix

Update translations

Add app shortcut (videos)

Translated using Weblate (Indonesian)

Currently translated at 100.0% (26 of 26 strings)

Translation: Just (Video) Player/Strings
Translate-URL: https://hosted.weblate.org/projects/just-player/strings/id/

Handle FF/RW keys

moneytoo#185

Update ExoPlayer to 2.15.1

Translated using Weblate (Turkish)

Currently translated at 100.0% (26 of 26 strings)

Translation: Just (Video) Player/Strings
Translate-URL: https://hosted.weblate.org/projects/just-player/strings/tr/

Update metadata

Translated using Weblate (French)

Currently translated at 100.0% (5 of 5 strings)

Translation: Just (Video) Player/Metadata
Translate-URL: https://hosted.weblate.org/projects/just-player/metadata/fr/

Translated using Weblate (Serbian)

Currently translated at 100.0% (5 of 5 strings)

Translation: Just (Video) Player/Metadata
Translate-URL: https://hosted.weblate.org/projects/just-player/metadata/sr/

Translated using Weblate (Portuguese)

Currently translated at 80.0% (4 of 5 strings)

Translation: Just (Video) Player/Metadata
Translate-URL: https://hosted.weblate.org/projects/just-player/metadata/pt/