Optimize T9Search performance / memory consumption

This change optimizes the T9Search feature in two ways:

1. Memory consumption
The original Contacts app actually crashed on my Vision with
an Out of Memory Error, until I increased the Heap Size to 48M
It was set to 32M before, and I cannot remember changing it before
so I guess, 32M is the default for Vision.

Now it works flawlessly with 32M again, mainly because it does not read
each and every contact's photo into RAM prior to searching,
but reads contact photos on demand/display.

2. Speed
The photo-reading task was not only memory- but also time-consuming,
and while doing so, the search just did not work. I always had to
wait a few seconds before typing in any number, else the search yielded
no results.

In addition to this I rewrote the name-to-number conversion. This
should also help speed-wise (yet not as much as the photo reading).

Actually the result is still no piece of art, but works how I expected
it to be -- I can hit the keys immediately after opening the Contacts
app, it immediately shows the correct results and it does not crash
with an OOM, even with a 32M heap size and ~400 contacts.

So this might actually fix #4922 as well.
http://code.google.com/p/cyanogenmod/issues/detail?id=4922

Change-Id: I90858354c7a718fe311a5e4f585a19a2972acc95