Global variables

[NChechulin]

First of all, I'd like to thank all the contributors for the work you have done.

However, I faced a couple of problems while I was setting everything up. For instance, the wifi interface on my laptop is called wlp2s0', not wlan0, my battery is called BAT0, not BAT1'.

I found myself replacing all of the "incorrect" names, which is not quite a good thing. My point is that it would be awesome if these names were stored in a single file so that one could change them all at once.