fixed custom command without selection does not run

Hi, I'm trying to customize the toolbar and run into this bug. The custom commands are not executed if no files are selected, even when the command does not contain keywords like $f, e.g. simply launch calc.

I added a method hasKeywordToken() in Command and used in CommandAction. Please let me know if this is not the right way to fix it.

PS: just want to say great work! I just started using it. And the latest transition to gradle made set up much easier.