Drop config option

Removes config option and alphabetical.json config, and tweaks location of the remaining one config file.

If the package is going to write to WP code standards, then it should be giving a canonical config for CSSComb, and not alternatives such as alphabetical. This is extra maintenance to keep in sync with the default.json and isn't to code standards (for what has been agreed for property ordering so far).

If folks want to use grunt-wp-css with custom ordering, then they can either have a `.csscomb.json` in their project root, or use grunt-csscomb directly with whatever config they want.

I see grunt-wp-css as being a way to bypass worrying about setting up CSSComb configs and doing custom replacements. It shouldn't therefore have the option.config or alphabetical.json, since it's then little more than a wrapper for CSSComb and the options it already has anyway.