Search bar filtering and sorting by file size in the file browser

as #12,

add UISearchDisplayController to FLEXFileBrowserTableViewController. and implement related methods for search.



If we make a non-concurrent operation and move this to the main method, we won't need to dispatch_async for this piece. The operation queue will dispatch the operation to the background. We will sill need to dispatch_async back to the main thread for the delegate call.