feat($goConnection): Enable deferred conn initialization 

@MaheshCasiraghi identified an issue whereby authentication could
only be performed during the Angular configuration stage.  The addition
of the `$connect` method now allows developers too configure, and connect
at any point in the life-cycle of their application.

Example:

```js
ourCoolApp.controller('sweetController', function($scope, $goKey, $goConnection) {
  var url = "https://goinstant.net/ACCOUNT_NAME/APP_NAME";
  var opts = { user: 'eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ...' };

  $goConnection.$connect(url, opts).then(function(c) {
    return c.room('lobby').join();
  }).then(function(result) {
    console.log(result.user);
  });

  $scope.todos = $goKey('todos');
  $scope.todos.$sync();
});
```