MediaCategoryViewController: Fix media deletion + Minor improvements
This merge request brings an adjustment to:
- The play queue that is scrolled to the currently playing item only if the current index is valid in order to avoid any exceptions.
- The currently playing cell's scroll view that now enabled allowing the user to delete it.
This merge request also brings a fix to the deletion of medias when the playback started with the following behaviours:
- If the media deleted is in the media list being played, the media list is updated as well as the play queue
- If the currently playing media is deleted, the media list and the play queue are updated and the next media in queue starts playing
- If the media deleted is not in the media list, no further action is performed.