context menu cleanup

context menu cleanup

changes:

video:
hide "update library" within or on video add-ons
hide "play from here" in context menu entries on scripts

music:
hide music related context menu entries on add-ons->"Get More..."
hide "update library" within or on video add-ons
hide "scan to library" in context menu entries on music->files->music add-ons
hide "switch media" in context menu entries within music plugin virtual folders

picture:
hide picture related context menu entries on add-ons->"Get More..."
hide "start slideshow( here)" in context menu entries on folders, zip, rar, cbz?, cbr?, scripts
hide "switch media" and "goto root" in context menu entries within or on picture plugins