Introduces custom template loader for my-{grouptype}s pages

Previously, these were handled by separate WordPress page templates: template-
my-courses.php, template-my-projects.php, etc. As per #505, these templates
have been combined into a single template for better efficiency.

However, moving them to a single template means that it no longer makes sense
to keep the current nomenclature for page templates. Moreover, the change
represents an opportunity to conform better to BP theme template location
conventions. So the operative template has been moved to:
    wp-content/themes/citytech/groups/index.php
and we are now filtering template_include to override the WP page template
selection process.