Adds publish/subscribe pattern to allow plugins and projects to hook into events (#55)

Also adds CLI to ease development.

packages/medusa-cli/src/util/version.js

@@ -0,0 +1,6 @@
+import { getMedusaVersion } from "medusa-core-utils"
+
+export const getLocalMedusaVersion = () => {
+  const version = getMedusaVersion()
+  return version
+}