Adds a application:config:dev setup rake task; clarifies README instructions.

* Adds rake application:config:dev to copy over example config files during initial setup.
* Switches to rails_config's `config/settings/<env>.yml` for per-environment config. (Excludes analytics settings from test.yml to avoid the GA key stuffing up the written-out-and-compared-with-PHP-output test fixtures.)
* Adds Ruby/Tidy/MySQL install instructions and the new rake task to README.