Files androidcontentdisposition

Commit 1:
- Moved content disposition code+workarounds to OCP\Response
- Added new OC\Response API called setContentDispositionHeader() that contains the needed workarounds for UTF8 and IE.
- Refactored download code to use the new API.
- Removed unused trashbin download file.

Commit 2:
Added Workaround for Android browsers in setContentDispositionHeader().
Fixes #5807 

Please review @karlitschek @DeepDiver1975 @schiesbn @kabum 

Note: I tried to write unit tests but PHPUnit is not happy when sending headers as it already sent some themselves, giving up for now.