Tell Hound to allow use of #find

And also prefer #find over #detect.
Refactor the ExtraMark model to be Rails 4 compatible

And also eliminate the need for the ExtraMark::UNITS hash lookup.
Second volley of Rails 4 model updates

This includes updating various queries for Rails 4 in a way that is
backwards compatible with Rails 3.

This also includes some small cleanups, and some model constraints
have been reordered to group the subject of the constraint.
Remove unused paramter variable
Remove unnecessary association query

A TA is a User. No need to query a user based on a TA's ID.
Fix spacing
Fix HTTP method for downloading spreadsheet CSV

`button_to` defaults to use HTTP POST whereas the
`download_grader_students_mapping` action is a GET action.

Tested:
- local server
Avoid n+1 queries in marks_graders view
Merge pull request #1669 from zhangsu/download_spreadsheet_grader_csv_method

Fix HTTP method for downloading spreadsheet CSV
Merge pull request #1661 from ferrous26/find

Tell Hound to allow use of #find
Merge pull request #1670 from zhangsu/spreadsheet_eager_assoc

Avoid n+1 queries in marks_graders view
Merge branch 'finders' of https://github.com/ferrous26/Markus into finders

Conflicts:
	app/controllers/results_controller.rb
Merged
Fix typo in comment
Fix indentation for EnforcedStyle key
Merge pull request #1672 from zhangsu/patch-1

Fix indentation for EnforcedStyle key
Merge pull request #1671 from zhangsu/patch-2

Fix typo in comment