Added a new class ConsoleApplicationTester, which during E2E tests
will create a separate isolated process for the Deployer to run in.
This class exposes methods for interacting with stdin and to grab
stdout, stderr and status code of finished process.
As well rename test dir to tests, as Pest does not support dir without s on the end.
Also, remove PHP requirement from composer.json as we already have check-in bin/dep and it's better to have the check only in one place (now they already out of sync).
