[Representation] Prefetch templates

...to ensure that dialogs et al can be displayed, even
after loss of network connectivity.

https://github.com/nasa/openmctweb/issues/383

platform/representation/src/TemplateLinker.js

@@ -54,7 +54,6 @@ define(
          * @param {string} the URL for the template
          * @returns {Promise.<string>} a promise for the HTML content of
          *          the template
-         * @private
          */
         TemplateLinker.prototype.load = function (templateUrl) {
             return this.$templateRequest(