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 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.

bmedx/modulestore,bmedx/modulestore,bmedx/modulestore