jsonrpc: expose specialsortseason and specialsortepisode for episodes
upnp: fix sort by upnp:rating
upnp: ignore "Unknown" as a single genre as it is added by Platinum
CDateTime: extend SetFromW3CDate() and add GetAsW3CDate(), GetAsW3CDateTime() and SetFromW3CDateTime()
upnp: fix serialization/deserialization of datetime properties
move ISliderCallback into its own header file
guilib: don't abuse and redeclare SPIN_CONTROL_TYPE_FOO
CGUISliderControl: fix SetIntValue() and SetFloatValue()
Merge pull request #4608 from Montellese/gui_slider_cleanup

CGUISliderControl: some cleanup and fixes
Merge pull request #4606 from Montellese/upnp_fixes

upnp: some fixes
Merge pull request #4596 from Montellese/jsonrpc_properties

jsonrpc: expose specialsortseason and specialsortepisode for episodes