Backport release to master

from Stanford-Online:release
into Stanford-Online:master
Add verification for CyberSource2 implementation.
Clean up shopping cart processor API.
Fix UUID JSON serialization bug in CyberSource2 implementation.
Update test suite to use new CyberSource2 implementation.
Fix i18n messages in CyberSource2
Enable CyberSource2 implementation by default.

Conflicts:
	lms/envs/dev.py
edx-west cybersource changes
Patch XSS vulnerability in Discussions

This ports the upstream patch [1] into our fork. This change is made
manually, instead of cherry-picking, as we currently lack the most
recent changes to the discussions product [2].

We will pick up the recent changes (and patch tests) the next time we
merge from upstream.

[1] https://github.com/edx/edx-platform/commit/58553a7fb8fbc33dfd40c8e7ca39b0f896fb5b32
[2] https://github.com/edx/edx-platform/commit/988e4e6da5bf5f8db1cb269a82cc272c6d73ed72
Merge pull request #121

from stvstnfrd:discuss/xss
into Stanford-Online:master
Merge pull request #120

from Stanford-Online:jbau/cybersource2
into Stanford-Online:master
Cut release candidate

from Stanford-Online:master
into Stanford-Online:rc
Release to production

from Stanford-Online:rc
into Stanford-Online:release