Add isvideo info for slideshow window.
Merge pull request #2565 from ulion/add_slideshow_isvideo_info

Add isvideo info for slideshow window.
videodb: use strings instead of numbers in videodb:// URL
CUPnPServer: fix bad videodb:// URL
musicdb: use strings instead of numbers in musicdb:// URL
videodb: add Filter parameter to GetSetsNav()
smartplaylists: add <group> to group the results on a higher level (e.g. genre, studio, director, ...)
CSmartPlaylistDirectory: add support for grouping to video smartplaylists
videolibrary: update library node XMLs to use the new grouping in smartplaylists
videodb: add GetItems() to retrieve a list of items of a specific type and media and GetItemById()
videodatabasedirectory: replace all the CDirectoryNode implementations that provide a list of grouped items with CDirectoryNodeGrouped
musicdb: support filtering in GetYearsNav()
musicdb: add GetItems() to retrieve a list of items of a specific type and GetItemById()
musicdatabasedirectory: replace all the CDirectoryNode implementations that provide a list of grouped items with CDirectoryNodeGrouped
CSmartPlaylistDirectory: add support for grouping to music smartplaylists
smartplaylists: add mixed grouping support
CSmartPlaylistDirectory: integrate mixed grouping
CGUIDialogSmartPlaylistEditor: integrate group options
CGUIWindowVideoBase: implement forced enabling/disabling of grouping into movie sets
[confluence] add controls for grouping in SmartPlaylistEditor.xml