opportunistically use Android's E164 cached numbers

The first call (and any calls if libphonenumber decides to clear out its memory cache) to canonicalizeNumber takes 700-950ms on my Nexus 5 due to the amount of metadata being read from disk. This leads to a pretty noticeable delay when opening a conversation sometimes.

This is a proposal that benefits devices on Jelly Bean or higher. Since API 16, Android provides E164 normalized numbers for any contact that has a number specified, and we can take advantage of that.