Major refactoring of ShoppinglistManager. It has been seperated into two classes, one responsible for all local actions (ListManager.java) concerning lists and listitems. And another responsible for all sync actions, of elements in the local database (ListSyncManager.java), this class runs on a completely seperate class, thus not disrupting any UI operations. This improves performance of both local and sync actions, and gives major improvements, in both maintainance and debugging of both classes.