[Request] Add custom command

[tonyrulez]

One thing I miss is the ability to add a custom application. For instance, I work with Google Spreadsheets, so I add them to the menu. On Windows, I can do this with PStart. This applet can only add apps from the list. Of course I can add custom things to the app list with kmenuedit, but then they'll show up in the standard menu too, and I can't hide them.

TLDR: add custom commands.