XBlock version 1.2.1

XBlock version 1.2.0

Merge pull request openedx#369 from edx/robrap/travis-pypi-deploy

Have Travis deploy to PyPI for new tags.

This tag was just used to ensure that Travis

would start building on tags.

CompletionXBlockMixin + tests (openedx#368)

CompletionXBlockMixin:

* Mixin itself
* Tests using hypothesis
* Added (or rather restored) ability to run single test via tox

Merge pull request openedx#365 from edx/efischer/play_nice_with_py27

remove unicode literals

Merge pull request openedx#349 from edx/cdyer/python3

Introduce python 3 compatibility.

Merge pull request openedx#362 from edx/cdyer/scorable-mixin

ScorableXBlockMixin

Merge pull request openedx#359 from edx/andya/use-web-fragments

Separate Fragment class out into new web-fragments package