supervisor-xserver: Add `XSERVER_LANG` variable to make `LANG` configurable
supervisor-xserver: Extract `xserver_gunicorn_workers` variable to defaults
supervisor-xserver: Move playbooks to supervisorctl and supervisor.conf
supervisor-xserver: Convert `xserver.conf` to supervisor configuration format
edxapp-perm-fixes: Make sure virtualenv exists before using python
edxapp-perm-fixes: Create directory for staticfiles with edxapp user
edxapp-perm-fixes: Stopped edxapp services only need to be started, not restarted
edxapp-perm-fixes: Ensure all edxapp venv files are readable by any user

For pip packages which create group-restricted venv files (httplib2).
edxapp-perm-fixes: Ensure edxapp/edxapp_worker are available in supervisor

Right after they are added for the first time, the commands are not available
until the groups are added.
supervisor-xserver: Switch from supervisor reloads to ansible "present" action

`supervisorctl reload` not only reloads the configuration files, but
also restarts all services, which causes all services to be reloaded
several times, and causes errors when the playbook later attempts to
start the services after changes have been applied.
Merge pull request #405 from antoviaque/edxapp-perm-fixes

Fixes for edxapp: Permissions & supervisor startup/configuration
Merge pull request #404 from antoviaque/supervisor-xserver

Move xserver to supervisor