Added bindings to the back/forward term buttons

Altered the load_exercises_page to take a shifting parameter, a value
with which to shift the term.
Merge branch 'master' of https://github.com/lmj112/classy-cate

Conflicts:
	views/classy_cate.coffee.erb
	views/exercises_page.haml
Implemented the next/back buttons for terms.

Sorted it so it doesn't fallback on holidays if you're deliberately
selecting them.