Redirect from engine root to features list.
Minor prettying and making it slightly more readable.

Fixed panel-group markup, sorted by enable status and name, got rid
of some of the labels and went to red/green list heading for features.
Which is how it was originally...
Protected method patrol.
Add inter-feature dependency.

Yes, you could do a circular dependency. It seems like overkill, but I
set this up in a real app and manually mentioned in three different
places that one feature wouldn't work until another one was enabled. Now
we can show that *and* have it affect the enablement status of the
feature.