Add ninjaframework example setup

* Adding the ninja demo app, or getting-started app, as a base to
  begin.
Add template and create/list feature

* Can now add todos and list them, from a veeeeery basic in-memory
  implementation - again being pragmatic about getting-it-to-work.
Add todos counter

* Adding the total todos counter, this does not yet account for
  filtering.
Add todo-filter handler

* Using the neat filter-feature, we can now add a filter to the
  session, always setting a proper filter for the todo list to
  show.
Add feature completeness

* Again a perhaps buggy but feature-complete example of the
  server-side todo app. This one was also a pleasure, man!
  The ninjaframework is expressive, relieved of cruft and
  put's the fun back into web app development.