merge from head
Merge branch 'master' of https://github.com/NZOI/nztrain

Changed stuff to make it work on my machine.

Conflicts:
	app/views/layouts/application.html.erb
Changed association between test cases and test sets

now it is a :has_many through a test_case_relation class.
Merge branch 'master' of https://github.com/NZOI/nztrain
Added migration for converting test cases to the new format.
revert temp. changes now that I have a working database
added down method on migration
added language model
create an association between languages and submissions
Merge branch 'master' of https://github.com/NZOI/nztrain into languages
added seeds for languages
fixed language migration
started adding judging helper class
Merge branch 'master' into judging-overhaul
add isolate installer
add isolock installer
add isolate service wrapper
use debootstrap ubuntu installation in isolate [ci skip]
remove ls command [ci skip]
force link recreation in isolate install [ci skip]