Blender Git Loki

Clean up in "add object" code:
* Get rid of ED_object_add_generic_invoke() and all invoke callbacks using it, it was doing nothing exec() callbacks would not do. In fact, its only action (setting part of common add ops properties, like loc, layers, etc.) was needed too by direct exec call, so it was done twice in case of using invoke()!
* Replace custom invoke code for metaballs by WM_menu_invoke helper (as already used by lamps).
* Add a new OBJECT_OT_empty_add op, to allow direct addition of empties of a given drawtype.
* And some general code cleanup (like trailing spaces, empty lines, ...).

Did quite a bunch of tests/verifications, but obviously could not tackle all possible scenarios... Anyway, if any, bugs should arize quite quickly (but I don�??t expect any! :p ).