Option to appear on primary display

[schnittchen]

I am a laptop user, I have one built-in monitor and attach to an external monitor when I can.

Apparently allocated X display numbers are not static. Depending on the configuration, after attaching an external monitor, it may become the new display 0, and the guake window will appear there when it used to do on the built-in monitor.

Guake allows to select the display number for its window. This feature makes sense for static display situations. The only thing that is static in my particular situation is the "primary display" flag.

The primary display is the one desktop shells use for their primary interface components. It would make sense for guake to do so (configurably) as well.

The configuration dialog already marks the primary display in the select input. I suggest adding an option "always on primary".

[schnittchen]

I made an effort, see #365

[gsemet]

great !

[gsemet]

Merged