rails3: don't load other locales unless we need/request them

test plan:
1. fire up your server
2. set your language to spanish
3. you should see english
4. fire up your server with RAILS_LOAD_ALL_LOCALES=true
5. set your language to spanish
6. you should see spanish

Change-Id: I7a7c3ef3dfd36c75d6d35b806d58ec8125798d92
Reviewed-on: https://gerrit.instructure.com/38452
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>
QA-Review: Jon Jensen <jon@instructure.com>