Adds schema caching capabilities (5s by default) (#2286)

* Adds schema caching capabilities (off by default)

* Use InMemoryCacheAdapter

* Uses proper adapter to generate a cache

* Fix bugs when running disabled cache

* nits

* nits

* Use options object instead of boolean

* Imrpove concurrency of loadSchema

* Adds testing with SCHEMA_CACHE_ON

* Use CacheController instead of generator

- Makes caching SchemaCache use a generated prefix
- Makes clearing the SchemaCache clear only the cached schema keys
- Enable cache by default (ttl 5s)

spec/Schema.spec.js

@@ -4,7 +4,7 @@ var Config = require('../src/Config');
 var SchemaController = require('../src/Controllers/SchemaController');
 var dd = require('deep-diff');
 
-var config = new Config('test');
+var config;
 
 var hasAllPODobject = () => {
   var obj = new Parse.Object('HasAllPOD');
@@ -20,6 +20,10 @@ var hasAllPODobject = () => {
 };
 
 describe('SchemaController', () => {
+  beforeEach(() => {
+    config = new Config('test');
+  });
+
   it('can validate one object', (done) => {
     config.database.loadSchema().then((schema) => {
       return schema.validateObject('TestObject', {a: 1, b: 'yo', c: false});