My favorite tool for changing Default Applications and/or Open With... options is the good old Ubuntu Tweak here:
Yes, it hasn't been updated for a long time, but it still works!
(Currently on Ubuntu 15.10)
Simply download and install this: https://launchpad.net/ubuntu-tweak/0.8.x/0.8.7/+download/ubuntu-tweak_0.8.7-1~trusty2_all.deb
Or add the PPA by tweaking for trusty.
Then you just need to start Ubuntu Tweak and go to Admins and then to File Type Manager, find the file type you need, double click on the entry, and there add/remove apps and/or set the default.
Make sure that files
contain the required entry, e.g.