Inherit Symfony pre-built assertions

[TavoNiievez]

Symfony already includes a large list of assertions.
module-symfony users should not have to give them up when deciding to use Codeception.

So this PR is an attempt to add to Codeception's $I-> syntax the assertions that are already built into Symfony, making the module a functional testing superset for Symfony rather than a replacement or competitor.

The obvious benefit of doing this is that people who already have tests in Symfony will find it easier to migrate to Codeception as it will not be necessary to spend time finding and rewriting tests in the Codeception equivalent of that assertion (where there is one).