Centerpiece - launcher

[siraht]

Please read the following before submitting:

• We are not accepting any new window management features unless they get implemented by i3.

Please fill out the following:

• Description:
  Please describe in plain English what the enhancement is and what the use case is.

I just found https://github.com/friedow/centerpiece and immediately wished it could be added to this project. I don't have an easy way to get onto IRC atm so thought I'd share here.