Redo Visit tab on patient dashboard to show grouped encounters

Each visit on the patient dashboard also needs to show the encounters that belong to it.

Possibly each visit row should have an expandable/collapsable [+/-] icon. (People generally don't like this UI though.)

Make sure that this doesn't slow down loading the patient dashboard--if necessary load the encounters in a second ajax query.

The first step of this ticket is to mock up a proposal, before doing anything.