Add method to clear mako template lookups

Quick and dirty fix (edxapp.startup.run is called twice, once before
loading the configuration, so the paths defined in lms.startup are
basically ignored).
Do not allow students to pin/unpin forum threads

The wrong permission was being checked for pinning/unpinning, so a
sufficiently clever student could pin and unpin threads.

JIRA: FOR-499
Make i18n tests quieter
pep8
Ensure that mongo modulestore can create its data directory if it does not exist on disk
refactor static tab tests
Merge pull request #2704 from edx/adam/refactor-static-tab-tests

refactor static tab tests
Ensure account creation succeeds before creating comments service user

Also improves handling in cases where account creation did succeed, but
comments service user creation did not.

Depends on commit 88abdd8a0b20bc9816f487b25abdea1953f5661d in https://github.com/edx/cs_comments_service

JIRA: FOR-522
Make all i18n scripts use argparse, handle --verbose flag
Added message to run during i18n tests to inform people that test_generate takes a long time
Merge pull request #2960 from edx/gprice/FOR-499

Do not allow students to pin/unpin forum threads
Merge pull request #2957 from edx/jsa/forum-user-sync

Ensure account creation succeeds before creating comments service user
Fix split_test import and export.

LMS-2405
reraise exception without changing traceback
Merge pull request #2840 from ionis-education-group/double-edxmako-startup

Add method to clear mako template lookups
mentoring-noworkbench: Remove import of workbench module (moved to SDK)
allow stderr if verbosity is off
tests only work when generate.main() is called with strict=False
in create_user mgmt command, use settings.LANGUAGE_CODE instead of en-us.

Fixes the create_user admin command, which was creating user accounts
with a potentially invalid language preference.

JIRA: FOR-532
Merge pull request #2973 from edx/diana/ab-import-export

Fix split_test import and export.