Added _model_InSongbook to cache information
Merge
Wrote add_song and remove_song functions in Songbook class; tests
merge
Continued add_song and remove_song functions in Songbook class; tests
Continued add_song and remove_song functions in Songbook class; tests with versionning
Adapt templates to *InSongbook; Fix importsongs
Merge branch 'master' of github.com:patacrep/songbook-web