change registration code email and attachments, per product requirements

[chrisndodge]

No description provided.

[chrisndodge]

@asadiqbal08 @muhhshoaib can you do a quick review of this? The product team has asked me to change the content of the email produced when one buys registration codes. We need to merge this by noon on Wednesday to make this week's release.

Thanks

[muhhshoaib]

should be blank line at end of file.

[muhhshoaib]

I have tested this branch locally and generated the invoice to see that the email templates are working fine. The Boychoy test was failing on Jenkins, i have started the manual test run for this PR.
Other than the pep8/pylint issues and a missing Docstring (not related to this PR) at https://github.com/edx/edx-platform/blob/cdodge/change-invoice-email-and-attachments/common/test/acceptance/pages/lms/dashboard.py#L23.
everything is looking good.

[chrisndodge]

Talked to @jzoldak about the failing bokchoy tests. He mentioned he's seen it in the past, but is not currently on the "known flakey tests" list. Merging with this in mind.

[jzoldak]

@chrisndodge FWIW I believe the test failure was actually due to #3747 which was merged and then maybe reverted? At any rate, it changed the dashboard.html template course section from "Current Courses" to "Courses" and the tests that failed are asserting on the esperanto translation of that string.

[jzoldak]

Further explanation regarding the failing LanguageTests in a comment on #5355.