Add Config model

* Add ability to configurably cache API responses per model
* Fix general error display on credentials
* Add current version from API to the documentation link

awx/ui/client/lib/models/index.js

@@ -1,4 +1,5 @@
 import Base from './Base';
+import Config from './Config';
 import Credential from './Credential';
 import CredentialType from './CredentialType';
 import Me from './Me';
@@ -7,6 +8,7 @@ import Organization from './Organization';
 angular
     .module('at.lib.models', [])
     .service('BaseModel', Base)
+    .service('ConfigModel', Config)
     .service('CredentialModel', Credential)
     .service('CredentialTypeModel', CredentialType)
     .service('MeModel', Me)