Rework user admin summary to use dedicated model and views

This reworked approach, using minimalist sub-views and sub-models to handle the updating and display of user summary info, avoids the need to re-render the whole users view, which in turn prevents the aw-snap issue encountered when manipulating multiple user accounts.

If Stats are shown and then a user is modified, the Stats view will re-render as hidden and the button class will be inverted.

A quick solution is to keep the Stats window visible if the button style has been toggled via the following in Thorax.Views.Users.initialize()

```
@collection.summary.on 'change', => @$('.stats-panel').toggleClass('hidden') if @$('.btn-toggle-stats').hasClass('btn-primary')
```