Unify lightbox views
Merge pull request #541 from sharetribe/lightbox

Unify lightbox views
Add condition to filter messages based on current community.
Update header to show unread messages only from current community.
Remove unused code.
Migrations and structure.sql.
Refactor to decrease db queries.
Add fragment caching to global header.
Move cached header code to own partials.
Add user id to cache key to prevent name collisions.
Remove unused method.