Add "AbstractCommand::getFromContainer($name)" method

[aik099]

The code for getting a dependency from container looks like this now:

$container = $this->getContainer();
$editor = $container['editor'];

Proposing to introduce helper method getFromContainer that would do that. After implementing above code will look like this:

$editor = $this->getFromContainer('editor');

Related to console-helpers/svn-buddy#97