add mock single-user server for testing
flesh out REST API

can now list/view/add/create/modify users
and start/stop single-user servers
update base page template

- no body params, just write jhapi globals instead
- baseUrl is static/js
some updates to login redirects

/anything served by Hub redirects to /hub/anything

/hub/user/[user] spawns single-user server and redirects to it
add basic home, admin pages

- index no longer requires login, it's just a big fat login button
- home has stop, start, admin buttons
- admin doesn't do anything yet
- add jhapi javascript client for REST API