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/Config.js

@@ -0,0 +1,32 @@
+let BaseModel;
+
+function getTruncatedVersion () {
+    let version;
+
+    try {
+        version = this.get('version').split('-')[0];
+    } catch (err) {
+        console.error(err);
+    }
+
+    return version;
+}
+  
+function ConfigModel (method, resource, graft) {
+    BaseModel.call(this, 'config', { cache: true });
+
+    this.Constructor = ConfigModel;
+    this.getTruncatedVersion = getTruncatedVersion;
+
+    return this.create(method, resource, graft);
+}
+
+function ConfigModelLoader (_BaseModel_) {
+    BaseModel = _BaseModel_;
+
+    return ConfigModel;
+}
+
+ConfigModelLoader.$inject = ['BaseModel'];
+
+export default ConfigModelLoader;