you can install controller on a raspberry pi with:
This is well documented and easy to follow
http://www.lowefamily.com.au/2016/06/02/installing-ubiquiti-unifi-controller-5-on-raspberry-pi/2/
in addition I suggest to install VNC server:
https://www.raspberrypi.org/documentation/remote-access/vnc/
now you can use your uniFi- controller either through VNC to the rPi desktop or directly in your browser https://rpi-ipnumber:8433 (*)
an thanks to Bollar for the hints
Karl
(*)the connection is insecure if you don't have a certificate system setup on your rpi. As long as you do things locally only it should not be a problem.