feat(plugins): Add initial version of ViewportPlugin class (#242)

* Add initial version of ViewportPlugin class
* Move entrypoints from OHIFPlugin to OHIF.plugins
* Add URL route to DICOMWeb server for Standalone Viewer

Packages/ohif-viewerbase/client/lib/classes/plugins/index.js

@@ -0,0 +1,18 @@
+import { OHIF } from 'meteor/ohif:core';
+
+import { OHIFPlugin } from './OHIFPlugin';
+import { ViewportPlugin } from './ViewportPlugin';
+
+// Each plugin registers an entry point function to be called
+// when the loading is complete.
+
+const plugins = {
+    OHIFPlugin,
+    ViewportPlugin,
+    entryPoints: {}
+};
+
+// TODO: When we reorganize the packages, we should figure out where to put this.
+OHIF.plugins = plugins;
+
+export default plugins;