Allow Guake to be assinged to Tasklist icon applet

[rbreaves]

I think the title is self explanatory, currently I just update it via gsettings and that works, but it appears to work sorta slowly. If you click it it flashes a lot and there's lag in it opening. Would love to see it not flash weirdly or launch slowly as it is doing (2-3 seconds) - pushing my hotkey F12 works much faster.

Reason I am requesting this is that I often remote into other desktops and when I do so my keyboard input gets captured away - aka F12 goes to my remote and does not stay local. I want to continue to use my local terminal and this option appears to work best (fastest).