Added Kontalk

I've added Kontalk to this. The icon was taken from the F-droid store page.

I figured that putting it first in the list of alternatives made most sense, as the first proprietary application listed was WhatsApp.

Sorry for some of the spacing, I tried to copy the spacing I saw used, but everything seems to be different. This project kinda needs some cleaning up, if I dare say it.

But well, I hope this is useful to you.