add a timer to quit the application

Fixes #385
Find dcmtk helper apps for test

Fixes #387

Discovery of helper apps had been in FindDCMTK.cmake, but was omitted
from a previous refactoring.  Since FindDCMTK.cmake may be obsoleted
in the future, the test cmake code now finds the apps directly.
Merge branch 'fix-failing-dicomapp-test'
Fix color dialog test that never quits

Remove timer to avoid race condition so that test quits after
dialog is shown.

Fixes #385
Merge branch '385-color-dialog-hang'