Adding support for "contact counts grouped by the first letter

of the sort key".

This is needed for two purposes:
1. To fix the A-Z index, specifically non-English ones and
address the issue of messed up index when sort order does not match
display order.

2. Take the first step toward the introduction of a scrolling
cursor.  When we have a scrolling cursor, we will _have_ to
build the index independently of fetching all of the data.

Bug: 2407129
Change-Id: Ie2979ff8e67446329ea6d1c2f5c9f4f215e6ec89