added "next" action message
PS: don't crash on null action
DDF: pass correct action to service
Changed player service notification id to 1
PS: foreground
PS: added onCompletion (for future use)
PS: rearranged, getInstance
PS: store playback queue
material: getUri
Material: use Uri.parse
Dance.getUri, etc
Dance: getUri: parse
Material: removed public constructor

Material may only be constructed from within Dance,
or else it will not have any data.
DataManager: get{Dance,Material}FromUri
Now material URIs seem to work
PS: implemented queue adding (partly)
DM: validate uri for being not-null