fixed: bug in OsmApi.getOsmApi()
cleanup: exception handling in interfacing with OSM API
new: new action for updating individual elements with the their current state on the server (including new menu item in the file menu)
new: improved user feedback in case of conflicts
new: handles 410 Gone conflicts when uploading a changeset
new: undoable command for "purging" a primitive from the current dataset (necessary if the primitive is already deleted on the server and the user wants to remove it from its local dataset)
new: undoable command for "undeleting" an already deleted primitive on the server (kind of "cloning")
new: after a full upload, checks whether there are primitives in the local dataset which might be deleted on the server.
new: data structures for history data
new: history download support in io package