Improvements for slow sorting roles

If the sorting is done for data which is resolved asynchronously
(e.g. rating), it is important to give a visual feedback about
the state of the sorting. This is done now by a progress
indication in the statusbar.

Also optimizations for "Sort by type" have been done: Although
resolving a type can be expensive in the most often case it is a
very cheap operation. So it the sorting is done by type, try
to resolve the type synchronously for at least 200 ms to prevent
a asynchronous resorting. This is usually sufficient to have
resolved types even for directories with several thousands of
items.


FIXED-IN: 4.9.0