Allow an user to signin/signup

resolves #1
We talked about using auto promise resolution like:

```javascript
$scope.user = UserService.get();
```

But it's no longer supported by angular, since the version `1.2.0-rc3`

> AngularJS 1.2.0-rc3 ferocious-twitch fixes a number of high priority issues in $compile and $animate and paves the way for 1.2. This release also introduces some important breaking changes that in some cases could break your directives and templates. Please be sure to read the changelog to understand these changes and learn how to migrate your code if needed
>
> due to 5dc35b52, $parse and templates in general will no longer automatically unwrap promises. This feature has been deprecated and if absolutely needed, it can be reenabled during transitional period via $parseProvider.unwrapPromises(true) api