Don't auto-generate Home nav menu link if one already exists

This changeset also refactors the way that these links are added, so that
the markup is created by WordPress directly.

See #1031
Correct "to skip this step" text during group creation. See #1035
Fix login redirect. See #1046
Add group type changing meta box. See #996
Add WP themes: Filtered, Hero. See #1036
Fix Group Profile link styling on herothemetrust theme. See #1036
Hide plugins from non-admin Plugins pages:

- cubepoints-buddypress-integration
- genesis-connect-for-buddypress

See #1048
Don't let Grader comments go to the activity stream

See #1050
Remove City Tech Student theme. Fixes #1047
Move home page template markup to template file
Basic responsive styling for home page
Responsive improvements for people directory
Responsive improvements on group directories
Responsive styling improvements for single group pages
Improve responsive styling on single member page
More responsive improvements. See #1043
Remove theme: Suffusion. See #988
Allow any group to have a Member Portfolios widget.

For non-courses, they are disabled by default.

See #1044
Add plugin: google-document-embedder. See #1060
Don't let the cropper get smaller than the avatar size

This prevents upsizing on very small images. See #1030