tmp commit to solve conflicts and help in PerformMusicSearchCommand
Partially completed PerformMusicSearchCommand,
fixed model (using id instead of another container) and method names,
fixed typo in Category class,
still to do for PerformMusicSearchCommand : search when peer is not a contact (MusicService), set Message parameters in NetworkService before calling sendUnicast method
IntegrateMusicSearchCommand must then read these parameters (see MessageHandler) and set them to the Command instance, then this command must append the results it contains to resultCatalog from appModel (don't clear this catalog before, this is already done in a previous command -MusicSearchommand- when sending the search request)