Fixing php7 pgsql package definition.
Adding mbstring and sqlite package definitions for php7.

This allows composer installs to function even if the installer checksum
changes, and doesn't force us to update the formula whenever their
installer changes.

We can do this now as composer upstream provides the checksum on
https://composer.github.io/installer.sig since 2016-04-28.

XML module is already built-in. In any case, `php5-xmlrpc` package actually provides XML-RPC module.

See README.rst for more information

The json features of php have been moved to a separate package in the following distributions:
  - Debian >= 8 (jessie)
  - Ubuntu >= 13.04

Changes:
  - Added json.sls
  - Updated map.jinja
  - Updated README.md

In RedHat, Fedora and CentOS mbstring and xml are not compiled by default in PHP
In Debian these are compiled by default so the generic php5 package was specified