Make ItemSync available as public API: - change id -> item mapping from usage of remoteId() to id() so clients can use ItemSync to create new items in Akonadi without having to fake a remoteId - install the header - remove the API dox declaring it as internal, also remove the comment about transactions since it is back to being a transaction.

@Volker: "local" and "remote" should probably be renamed

svn path=/trunk/KDE/kdepim/akonadi/libakonadi/; revision=772470