[BUG] Sorting a sorted RLMArray

Core's `Query::tableview` method should not be used as it does not support sorting a sorted view. 

See also https://github.com/willmoore/RealmTest for original bug report.

@alazier @tgoyne @jpsim 
you wouldn't need to rewrite it 4 times, just change the helper to `- (void)sortEmployeesByAgeAscending:(BOOL)ageAscending nameAscending:(BOOL)nameAscending`. It would then take `self` implicitly.