Refactor some more models

Grouping attribute constraints, and updating some queries for Rails 4.
fix grader in criteria checkbox bug
scope, props refactor for students_table
scope, props refactor in groups manager
basic refactor for submissions table
move stuff to default props in summaries table
add some comments to graders manager
make session store point to config settings
ok, now fixed selected all criteria
Hound complaints
Fix method name in markus:load:results

The method has been renamed to `update_results_stats`, but the invocation in the task is not updated.
move over http links to https
fix url paths for ajax GET calls
remove user_params for admins and students#new
style fix
fix asset paths for react images (add_arrow, etc)
Use image assets for asc/dec arrows in tables
Fix descending column class