Option to ignore parse file storage (#2222)

* flag in configurations to use only files adapter

* added lib folder

* remove lib

* alignment edit

* replace comma with semicolon

* ignore parse file storage if fileKey is not provided (undefined)

src/ParseServer.js

@@ -109,7 +109,7 @@ class ParseServer {
     dotNetKey,
     restAPIKey,
     webhookKey,
-    fileKey = 'invalid-file-key',
+    fileKey = undefined,
     facebookAppIds = [],
     enableAnonymousUsers = true,
     allowClientClassCreation = true,