Split client and server plugin functionality.

There is virtually no shared code for the client, extract it into its own
module and do away with the switches.

src/static/js/pluginfw/client_plugins.js

@@ -0,0 +1,36 @@
+var $, jQuery;
+$ = jQuery = require("ep_etherpad-lite/static/js/rjquery").$;
+var _ = require("underscore");
+
+var pluginUtils = require('./shared');
+
+exports.loaded = false;
+exports.plugins = {};
+exports.parts = [];
+exports.hooks = {};
+exports.baseURL = '';
+
+exports.ensure = function (cb) {
+  if (!exports.loaded)
+    exports.update(cb);
+  else
+    cb();
+};
+
+exports.update = function (cb) {
+  // It appears that this response (see #620) may interrupt the current thread
+  // of execution on Firefox. This schedules the response in the run-loop,
+  // which appears to fix the issue.
+  var callback = function () {setTimeout(cb, 0);};
+
+  jQuery.getJSON(exports.baseURL + 'pluginfw/plugin-definitions.json', function(data) {
+    exports.plugins = data.plugins;
+    exports.parts = data.parts;
+    exports.hooks = pluginUtils.extractHooks(exports.parts, "client_hooks");
+    exports.loaded = true;
+    callback();
+   }).error(function(xhr, s, err){
+     console.error("Failed to load plugin-definitions: " + err);
+     callback();
+   });
+};