Remove collection prefix and default mongo URI (#1479)

* Remove collection prefix from DB Controller

* Remove collection prefix from cache

* Revert "Remove collection prefix from cache"

This reverts commit 529d67dd617b64c69c36a8a63382456e95edcab8.

* Remove knowledge of default mongo URI from Parse Server

* Remove adaptive collection paramater from deleteFields

* Tidy up DBAdapter.js

src/Adapters/Files/GridStoreAdapter.js

@@ -7,13 +7,15 @@
  */
 
 import { MongoClient, GridStore, Db} from 'mongodb';
-import { FilesAdapter } from './FilesAdapter';
+import { FilesAdapter }              from './FilesAdapter';
+
+const DefaultMongoURI = 'mongodb://localhost:27017/parse';
 
 export class GridStoreAdapter extends FilesAdapter {
   _databaseURI: string;
   _connectionPromise: Promise<Db>;
 
-  constructor(mongoDatabaseURI: string) {
+  constructor(mongoDatabaseURI = DefaultMongoURI) {
     super();
     this._databaseURI = mongoDatabaseURI;
     this._connect();