Add a 'string literal' serialization method and use it in the lambda function mapping table when the value to xml serialize is of basestring type. Also a couple of drive-by pep8 fixes.
add new tests for the string literal serialization
fix up some of the test courses which had hardcoded that quot; escaping
use better syntax for asserting that exception is thrown
raise a more appropriate Exception
change serialize_field to check for type. If value is a string, simply return that, otherwise do a json.dumps
Merge pull request #387 from edx/fix/cdodge/unescape-quote-strings

[STUD-406] Fix/cdodge/unescape quote strings