Refactor email assertions

[TavoNiievez]

In this PR:

• Support for Swift Mailer is removed.
• The mailer: config parameter is removed since it is no longer needed.
• Now it is possible to assert emails sent from Symfony commands.
• The Profiler is replaced by Mail Logger to do the email assertions since the profiler requires 'requests' to be made and that is not always a requirement to send emails in Symfony.

The fewest possible changes were made to the API to make it easier for users to upgrade to version 2.

The most significant change, however, is that seeEmailIsSent now defaults to 1 instead of null. This change is made because previously an assert of type assertGreatherThan was made, whereas now, the EmailCount Constraint requires that the expected number of emails be specified.

Checking the exact amount of emails sent is probably what you want to assert in your tests.

[TavoNiievez]

@ThomasLandauer please review this.

This fixes your issue Codeception/Codeception#4698 so I am complying with what is mentioned in #24 (comment)