Revert change ca9f8a7036 that converted
text in Add Application -dialog to rich text. The text is plain
text and doesn't use any formatting so plain text is good for it.
Get rid of the form layout stretching the Browse-button so wide. Use
form-like but more flexible layout. Change the term 'Application to
execute' to 'Command to execute'. This reduces duplication and makes
clear difference between application name and the command to execute
to start the application. Fix also tab ordering so that the
application name field gets the focus initially.