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/Postgres/PostgresStorageAdapter.js

@@ -959,10 +959,6 @@ export class PostgresStorageAdapter implements StorageAdapter {
       });
   }
 
-  dropDatabase() {
-    return this.deleteAllClasses();
-  }
-
   // Remove the column and all the data. For Relations, the _Join collection is handled
   // specially, this function does not delete _Join columns. It should, however, indicate
   // that the relation fields does not exist anymore. In mongo, this means removing it from