Improve attribute tagging on unit tests

* Mark slow tests as 'slow'
* Mark selenium tests as 'slow'
* Correspondingly update the unit testing wiki page with more about
  attribute usage
Disable Exam 'Save Answers' button during saving

* Closes #1903
Disable exam 'check answers' button during checks
Remove CRLF line endings everywhere they appear

* Nothing else touched in this commit
* Produced by running the following:
    for file in `find . -iname '*.py' -o -iname '*.txt' -o -iname '*.html' -exec file {} \; | grep CRLF | cut -d':' -f1`; do
        dos2unix $file; git add $file;
    done && C2G_HEADLESS_TESTS=1 REUSE_DB=1 ./manage.py test -v 2 && git commit
Re-enable save answers button on success

* Rather than re-enabling the save answers button when the user exits
  the message dialogue, re-enable it on XHR success.
Merge pull request #2118 from Stanford-Online/jrbl-1903-disable-exam-buttons-during-ajax

Disable Exam 'Save Answers' button during saving
Merge pull request #2161 from Stanford-Online/jrbl-2125-jrbl-hates-crlf

Remove CRLF line endings everywhere they appear
Merge pull request #2160 from Stanford-Online/jrbl-attrs-for-tests

Improve attribute tagging on unit tests
Minor cleanups to exam listAll
Merge pull request #2164 from Stanford-Online/jrbl-exam_listing_cleanups

Minor cleanups to exam listAll
Add readonly section (#1441)
Merge branch 'master' of https://github.com/Stanford-Online/class2go into giulio-retinize-2155
commented out sticky footer for now