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

Also adds CLI to ease development.

packages/medusa/package.json

@@ -38,6 +38,12 @@
     "serve": "node dist/app.js",
     "test": "jest"
   },
+  "peerDependencies": {
+    "medusa-interfaces": "^0.3.0"
+  },
+  "peerDependencies": {
+    "mongoose": "5.x"
+  },
   "dependencies": {
     "@babel/plugin-transform-classes": "^7.9.5",
     "@hapi/joi": "^16.1.8",
@@ -47,7 +53,6 @@
     "bull": "^3.12.1",
     "client-sessions": "^0.8.0",
     "cookie-parser": "^1.4.4",
-    "core-js": "^3.4.8",
     "cors": "^2.8.5",
     "dotenv": "^8.2.0",
     "express": "^4.17.1",
@@ -57,15 +62,13 @@
     "joi-objectid": "^3.0.1",
     "jsonwebtoken": "^8.5.1",
     "medusa-core-utils": "^0.3.0",
-    "medusa-interfaces": "^0.3.0",
+    "medusa-interfaces": "^0.1.27",
     "medusa-test-utils": "^0.3.0",
-    "mongoose": "^5.8.0",
     "morgan": "^1.9.1",
     "passport": "^0.4.0",
     "passport-http-bearer": "^1.0.1",
     "passport-jwt": "^4.0.0",
     "passport-local": "^1.0.0",
-    "regenerator-runtime": "^0.13.3",
     "winston": "^3.2.1"
   },
   "gitHead": "35e0930650d5f4aedf2610749cd131ae8b7e17cc"