Besides MPRIS support, this also adds support for hasPrevious() and
hasNext() in several parts to determine whether the
player/playlist/shuffler has a previous or next item.
* Properly keep track of the current offset and total recourd count in
models.
* Catch exceptions and store them in errorString properties wherever
applicable in loaders.
- Removed "jellyfin" prefix from files, as they are already in a
directory named Jellyfin
- Split the former "jellyfinitem.{h,cpp}" into multiple files in the DTO
directory, one for each class. The jellyfinitem files started to
become enormous.
- Use forward declarations in headers instead of including files
wherever possible.
- Updated copyright headers
- PlaybackManager now takes ownership of set items
- PlaybackManager can play items just by their itemId, avoids useless
item creation on the QML side of things.
- Allow calling Jellyfin::registerTypes with a different URI
- Minor code cleanup