Add a dmenu/rofi keybinding for default config

[lgsobalvarro]

In a similar way as standalonetray has being implemented into the default config file, it could be a nice touch if there was also a keybinding to call dmenu and/or rofi. Eg:

Key Space A M Exec exec dmenu_run

Or perhaps a menu option in a similar fashion as wmaker's "run command" window works. However I think this method could be considered a bit silly.

[ThomasAdam]

Hi @lgsobalvarro,

Thanks -- if you want to open a PR with a patch, that'd be good.

Kindly,
Thomas