Improve phone number formatting and caching

Phone number parsing and formatting is difficult. Furthermore, tel links
can be sensitive. These changes save the best formatting efforts and
also the best version of the digits only.

We first use Fakie to attempt to parse the user input. If it succeeds,
we save the parsed number in the number field (with local or
international formatting depending on the number). We save the e164
version in the digits field complete with the + symbol prefix.

A tel_url helper strips the +1 off for national calls. For international
calls it replaces the + symbol with 011. For numbers without the +
prefix, it just passes the digits as-is.

This is currently very US centric. Suggestion for future changes.
Include country-code in the account set up. Use the country code to
split between local_format and international_format and to correctly set
up tel_url.