Hopefully fix the html validation test

The /admin page now needs admin authorisation
Fix missing decl of required template file
Use local type with derived JSON instances for user group resource
Improve user put/delete handlers
Add a more comments to the user feature handlers
Rename user feature serve functions
Extend json responses for user resources
Move a couple resource handlers from html to user feature

Previously the user feature didn't serve the get/put/delete methods
directly but exported methods that the html feature used to implement
them with html responses. Move it around so it's sane: methods using
JSON formats in the user feature and no wrappers in the html feature.
Use in html pages relies on the form wrappers stuff.
Tidy up the form wrapper code