Merge pull request #3 from aronasorman/master

Build language packs for release-0.11 central server
Merge pull request #4 from aronasorman/master

adding in crowdin vars for update_language_packs
Added "update_kalite" tags, and reordered some tasks.
Added Khan API token/secret loading.
Moved DISQUS_USER_API_KEY setting to be set only if defined in secrets
Add alias for media directory to be served directly by Apache
Put keep on 0.11.1 branch and update Postmark sender address.
Make gatehouse 'when' clauses work with dry runs
Nginx proxy config more flexible, allow selective https enforcement
Update keep to use ka-lite master branch
Add sudo_user for language pack building
Add grunt installation and build process to fle-site
Add fixture-loading for fle-site (commented out)
Added cron jobs for building language packs every 2 weeks.
Copy in a pre-computed initial srts_remote_availability.json file.
Incorporated admin account creation and SSH key reg into server role.
Allow ufw to be disabled on a per-host basis.
Changing variable names ka_lite_* to ka_lite_central_*
Change paths to new central server structure.
Change _kalite_ variables to _ka_lite_central_