Index, create, view working

and very close to having edit, delete working as well.
Update, delete working for Step 4

after reading the MongoDB driver docs a bit more thoroughly. A few
challenges faced to this point:

- Serving static resources is not trivial. Ultimately, I needed the
  <base> tag to use the right root context, since it's also apparently
  difficult to tell Spring to serve this at /.
- HiddenHttpMethodFilter handles POST-as-PUT, POST-as-DELETE, etc. via
  the usual _method parameter trick. It has to be manually enabled in
  web.xml by creating a <filter-mapping>.
- @ModelAttribute doesn't appear to pull {id} @PathVariables. This might
  be because the underlying object attribute in MongoDB is '_id', not
  'id', but I'm not sure. A quick workaround is to use @PathVariable
  and a findById() call.
- mongo.insert() doesn't update; you need mongo.save() for that.
- mongo.insert(), mongo.remove(), and mongo.save() need to have the
  same collection name supplied, unless you go with the default
  class-based collection names.
  
A bunch of these difficulties are MongoDB-related, but they still touch
on bits of the SpringMVC stack (@PathVariable vs. @ModelAttribute, for
instance.) Still learning...