Hide individual launchers for ebook-edit, ebook-viewer and lrfviewer
    
    ... as discussed with nirik and hughsie on IRC.
    
    Shipping several launchers in one package breaks GNOME and KDE software
    center applications that expect to have one app launcher == one package.
    
    To fix this, this commit hides the ebook-edit, ebook-viewer and
    lrfviewer launchers and drops their appdata. They are really internal
    implementation details of the main calibre GUI that already provides
    buttons to launch these.