Expose dimensions on InternalApp
Remove unslotted_elements (as in master)
Fix rotate regression (remember rotate)
Refer to top_slot on InternalApp
Update rake samples task

Now displays index and total on each run. Also allows you to specify an
arbitrary file in samples/ as a source of samples to run (not just
README). Use like

    rake samples[CUSTOM]

to run samples listed in samples/CUSTOM
Modify sample19.rb (remove unnecessary layout call)
Wire up click between App, InternalApp
Move textcursor code up the stack
Remove unneeded adjustments to minesweeper
Update textcursor specs