Even faster tests (#4868)

* Various improvements in test name / de-duplications

* Reverts to class by class deletion, introduced fast mode that just delete data for mongo

- Speeds up are incredible Executed 1695 of 1713 specs INCOMPLETE (18 PENDING) in 4 mins 19 secs.

* Adds documentation about the deleteEverything

src/Adapters/Storage/StorageAdapter.js

@@ -31,7 +31,7 @@ export interface StorageAdapter {
   createClass(className: string, schema: SchemaType): Promise<void>;
   addFieldIfNotExists(className: string, fieldName: string, type: any): Promise<void>;
   deleteClass(className: string): Promise<void>;
-  dropDatabase(): Promise<void>;
+  deleteAllClasses(fast: boolean): Promise<void>;
   deleteFields(className: string, schema: SchemaType, fieldNames: Array<string>): Promise<void>;
   getAllClasses(): Promise<StorageClass[]>;
   getClass(className: string): Promise<StorageClass>;