fix rake db:initial_setup bug

always load models alphabetically, and remove unnecessary load paths.

Dir.glob doesn't guarantee an order (it uses readdir(3)), so on some
platforms quizzes/quiz_question/numerical_question.rb could load
before quizzes/quiz_question/base.rb.

when coupled with rails' automagical directory->module inference,
NumericalQuestion would try to subclass ::Base (not having found a Base in
in quizzy land), which it cannot do since it's a module. ::Base was auto-
created due to the existence of app/stylesheets/base.

test plan:
1. try to run `rake db:initial_setup` on ubuntu 14.04
2. it should succeed

Change-Id: I534c5a0755671a0f3aa6ee96236596dfa733aa86
Reviewed-on: https://gerrit.instructure.com/38797
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>