handle checkout of theme repo
add symlinks in edx-west dir

Conflicts:
	playbooks/edx-west/edxapp_prod.yml
	playbooks/edx-west/files
	playbooks/edx-west/group_vars
	playbooks/edx-west/roles
Add theming support to edxapp role and refactor some handlers

Handler changes:
- add one main handler which invokes all other handlers
- "restart" on edxapp does not work, so split into stop and start
restart -> stop+start
add deploy tag edx-platform git checkout task