Add option to re-use schema cache between requests (#2979)

* Add option to reuse database controller between requests. Clear schema cache when deleting everything

* Add test

* Rename setting to persistSchemaCache to more accurately reflect effect

* Repurpose option to determine whether to randomize cache prefix. Restore Config.js controller creation. Add tests

* Fix bug with missing parameter passed to to SchemaCache

* Renaming and formatting

* Fix property name typo

* Rename option to avoid double negative and still be falsey by default. Style fix

src/Controllers/DatabaseController.js

@@ -515,7 +515,10 @@ DatabaseController.prototype.canAddField = function(schema, className, object, a
 // Returns a promise.
 DatabaseController.prototype.deleteEverything = function() {
   this.schemaPromise = null;
-  return this.adapter.deleteAllClasses();
+  return Promise.all([
+    this.adapter.deleteAllClasses(),
+    this.schemaCache.clear()
+  ]);
 };
 
 // Finds the keys in a query. Returns a Set. REST format only