Basic support for Google Drive & OAuth.
Merge branch 'master' into drive

Conflicts:
	data/data.qrc
Almost working tagging from stream.
Hacky support for reading tags from MP3s on Google Drive.
Requires TagLib 1.8
Cache taglib Drive requests in a google::sparsetable.
Requires sparsehash.
Add URL handler for googledrive URLs and fetch a new temporary
download URL for every play.
Refresh oauth token when possible to avoid reauthenticating with Drive
all the time.
Make Google Drive support optional and add a cmake option for it
Make Google Drive option available as #define.
Index Google Drive MP3s and write to local database.
Show a nicer success page when oauth is complete.
Move some of the Google Drive bits out into a separate client class.
Read Google Drive metadata in the tagreader worker process
Add a new PlayBehaviour (MultiplesItems) for loading playlits' songs by drag'n'drop for Internet services.
Use it for Spotify and Grooveshark.
Add a separator after custom playlist item' actions
Add a more descriptive text for "Remove duplicates" action, and display it in the same way in the Playlist menu and the playlist item right click menu.
Create the playlistiem_actions separator only once (to avoid a memory leak introduced in revision a38be50b0058: as the actions are supposed to be owned by the internet service, the separator action added in main window wasn't deleted).
Add a directory model for selecting a default upload directory on Google Drive.
Add "append to/replace/... playlist" and "Configure" actions to Spotify items.
Automatic merge of translations from Transifex (https://www.transifex.net/projects/p/clementine/resource/clementineplayer)