I have tried a number of Ubuntu version and none of them seem to support the EDIMAX wifi dongles. In general I hate Xenial Xerus releases as they screw to much with how wifi works (or not).
Most successful Wifi instructions are based on 14.04, which is a better OS in my opinion. Such as http://blog.gavinadams.org/2015/02/01/beaglebone-black-with-edimax-usb-wi-fi-on-ubuntu-14-04/
But 2015 seems to be missing from the https://rcn-ee.net/rootfs/ directory
Where did it go Mr Nelson?