This is because we can no longer assume a one to one mapping between roster
contacts and their views. Roster contacts can belong to more than one group,
each group needs to show the contact, which means we need a view for each group
the contact belongs to.

updates #83

In order to make group values non-distinct, (i.e. buddies can be in multiple
groups), we can't assume there's one view per roster item.

This means we cannot manage the rosterview as an overview (since it makes this
assumption).

updates #83

updates #83

updates #83

by moving event handers out

* Differentiate between adding new roster items and rendering existing ones.
* Also, only sort pending and requesting contacts once they've all been added
  (similar to what was already being done with existing contacts)

Simplified updateRoster by removing the duplicate checks that RosterItemView's
render method was doing.

Can't know whether existing roster item is already shown under the existing group.

But other user is not online to quickly subscribe back.

Conflicts:
	converse.js

Assignment to writable property `style.height` instead of readonly `offsetHeight`.

Fixes #196.

Make sure contact's chat_status attr is saved.

Updates #175

Make sure contact's chat_status attr is saved.

Updates #175

Made sure that the non-group usecase is still covered.