Query bus plugins cannot add to the chain.

[bweston92]

Consider the following:

// It currently does this.
$deferred = new Deferred();
$promise = $deferred->promise();

$promise->then(function ($a) {
  return strtoupper($a);
});

$promise->done(function ($a) {
  // $a = 'hey;
});

$deferred->resolve('a');

// We need to do this.
$deferred = new Deferred();
$promise = $deferred->promise();

$promise->then(function ($a) {
  return strtoupper($a);
})->done(function ($a) {
  // $a = 'HEY;
});

$deferred->resolve('a');

We need to set the promise on the action event and then allow plugins to add to the chain updating the action events promise with the last chain and return that.

[codeliner]

Fixed with #98