Loads a settings file and sets appropriate options. Used to determine
whether or not we should completely override a style in a theme

@param {string} source The source of the settings file to load
@param {Object} ctx The given context to set our options
@return {Promise}
function loadSettings(source, ctx) {
  return loadSingle(source).then(function (data) {
    if (data) {
      data = JSON.parse(data);
      ctx.override = data.override;
    }
  });
}