Add `grunt-shopify-theme-settings` plugin and generate first pass at theme settings.
Bump required version of grunt plugin to access `default` feature.
Break settings.yml out into individually ordered YAML files.
Few tweaks to bring new settings in line with old ones.
Bump required version of Grunt plugin to enable empty <option> tags in settings.
Pick up new settings from master, fix rebase merge issue.
Merge pull request #205 from gavinballard/grunt_shopify_theme_settings

Closes #186 - Use Grunt plugin to manage theme settings.