function resolveIfPluginHas(optPath, propName, plugin) {
    var opt = plugin.getIn(optPath);
    if (opt.size) {
        return plugin.set(
            propName,
            resolvePluginFiles(opt, plugin.get("relpath"))
        );
    }
    return plugin;
}
If a plugin contains this option path, resolve/read the files
@param {Array} optPath - How to access the collection
@param {String} propName - Key for property access
@param {Immutable.Map} plugin
@returns {*}