wp-config.php cleanup

[ataylorme]

wp-config.php needs some love. Currently a lot of items are repeated between local/non-Pantheon and Pantheon environments.

We should cleanup wp-config.php so that all shared items live in the main file and Pantheon or local specific items are separated out into wp-config-pantheon.php and wp-config-local.php respectively.

These files can then be included based on whether $_ENV['PANTHEON_ENVIRONMENT'] is present or not.

wp-config.php should also follow WordPress coding standards and be run through code sniffing