Finish basic UI:

* Finish widgets for size and file type stuff

* Reorganize toolbar and menus

* Complete implementation of three interface styles; link to property
box.

* Move add/remove stuff

* Generate command-line for back end.


Finish back end:

* Core is done, implement predicate parsing/execution.

* Optionally output to gmc window.

* Optionally show progress dialog (update only on new dir, not each
new file, else would be too slow).


Spit & Polish:

* Add accelerators

* Add help (including pervasive popup help).

