Fix detection of nette/application

[enumag]

Currently some of my tests are failing with

[Nette\DI\MissingServiceException] Service 'application' not found.

because I have nette/application in dev dependencies but don't use it in all the tests. The problem occurs if a test uses ConsoleExtension without ApplicationExtension.

@fprochazka Should I refactor it to a property like I did here? Personally I like it better than a method.

[fprochazka]

@enumag yeah, this way it's more logical. The property is faster, but the method is imho cleaner. And you can always add the property inside the check method, to make it faster, if that's needed.

[enumag]

@fprochazka Speed is not relevant here so let's leave it as is.

[fprochazka]

Thank you!