ObjectContext API to use varargs

It is quite annoying to wrap objects in collections to invalidate objects... This is easily solved with varargs. For symmetry we can do the same with with deleteObjects. So we'll end up with:

void invalidateObjects(Collection<?> objects);
void invalidateObjects(Object... objects);

void deleteObjects(Collection<?> objects);
void deleteObjects(Object... objects);

@Deprecated // redundant
deleteObject(Object object);