Translate strings in xmodule/capa_*.py

LMS-1744
i18n of common/lib/capa/capa files

Also pep8, pylint, and style fixes
Covers:
{capa_problem, correctmap, customerender,
inputtypes, responsetypes, util, xqueue_interface}.py
LMS-1744
Merge pull request #2219 from edx/sarina/i19-capa-new

i19 base capa strings