Change the default dir for loading xml files.
This should always be overridden by the testcases if needed.
Do not create a modulestore unnecessarily in tests
Implements keyword sub feature for bulk emails

This commit pulls in changes from #4487 that implements keyword
substitution for bulk emails. With these changes, an instructor can
include keywords in their bulk emails which will be automatically substituted
with the corresponding value for the recepient of the email. Keywords are
of the form %%keyword%%, and the keywords implemented in this commit include:

%%USER_ID%% => anonymous_user_id
%%USER_FULLNAME%% => user profile name
%%COURSE_DISPLAY_NAME%% => display name of the course
%%COURSE_END_DATE%% => end date of the course

Client-side validations have also been implemented to ensure that only emails
with well-formed keywords can be sent.
The architecture is designed such that adding in new keywords in the future
would be relatively straight-forward.
Don't break up i18n string
Double quotes for i18n string
Merge pull request #6111 from edx/zoldak/modulestore-test-config

Unit test speed improvements
Replace &mdash; with literal emdash
Merge pull request #6225 from edx/studio-i18n-improvements

Don't break up i18n string
Change openedx footer image to a non-broken link
Merge pull request #5449 from Stanford-Online/njdup/bulk_emails_keyword_sub

Implements keyword sub feature for bulk emails
Merge pull request #6230 from edx/sarina/fix-openedx-logo

Change openedx footer image to a non-broken link