Reintegrate the PluginHelper

Reintegrate the PluginHelper and provide it to the plugins via the
plugin loader as requested by @aldipower. For details about this
decision please refer to
https://github.com/mesosphere/marathon-ui/pull/609/files#r52335225

src/js/plugin/PluginLoader.js

@@ -5,6 +5,7 @@ import PluginDispatcher from "./external/PluginDispatcher";
 import PluginEvents from "./external/PluginEvents";
 import PluginMountPoints from "./external/PluginMountPoints";
 import PluginActions from "./external/PluginActions";
+import PluginHelper from "./external/PluginHelper";
 import PluginDispatcherProxy from "./PluginDispatcherProxy";
 
 const PLUGIN_STARTUP_TIMEOUT = 10000; // in ms
@@ -39,6 +40,7 @@ const PluginLoader = {
           PluginActions: PluginActions,
           PluginDispatcher: PluginDispatcherProxy.create(pluginId),
           PluginEvents: PluginEvents,
+          PluginHelper: PluginHelper.create(pluginId),
           PluginMountPoints: PluginMountPoints,
           pluginId: pluginId,
           UIVersion: config.version

src/js/plugin/external/PluginHelper.js

@@ -0,0 +1,41 @@
+import PluginDispatcher from "./PluginDispatcher";
+import PluginEvents from "./PluginEvents";
+
+export default class PluginHelper {
+
+  constructor(pluginId) {
+    this.pluginId = pluginId;
+    Object.freeze(this);
+  }
+
+  static create(pluginId) {
+    return new PluginHelper(pluginId);
+  };
+
+  callAction(action, data) {
+    PluginDispatcher.dispatch({
+      actionType: action,
+      pluginId: this.pluginId,
+      data: data
+    });
+  }
+
+  injectComponent(component, placeId) {
+    PluginDispatcher.dispatch({
+      eventType: PluginEvents.INJECT_COMPONENT,
+      placeId: placeId,
+      pluginId: this.pluginId,
+      component: component
+    });
+  }
+
+  registerMe() {
+    PluginDispatcher.dispatch({
+      pluginId: this.pluginId,
+      eventType: PluginEvents.STARTUP_COMPLETE
+    });
+  }
+
+}
+
+export default PluginHelper;