Move mailgun adapter to it's own repo

Author: drew-gross

package.json

@@ -36,6 +36,7 @@
     "multer": "^1.1.0",
     "node-gcm": "^0.14.0",
     "parse": "^1.8.0",
+    "parse-server-simple-mailgun-adapter": "0.0.1",
     "redis": "^2.5.0-1",
     "request": "^2.65.0",
     "tv4": "^1.2.7",