Allow Consequences on Fixture methods

[ricardorlg]

@wakaleo currently Serenity allows to execute of Screenplay Actions on After methods even if a previous step has failed, but Consequences are not executed, I already have a fix for this, but this opens a new window, Can we allow Tasks executed on After methods to don't mark the Test as failed in case an error happens when performing it.

I have a possible PR to allow this, but I would like to know if you think I should allow this using a specific Serenity property in order to don't affect other folks that don't want that behavior.

Also now we allow the call of the attemptsTo method using the IGNORE_EXCEPTIONS flag, but I think that flag is not completely true, at the end of the performable throws an exception the Step is marked as failed, what do you think if I add a way to allow Tasks to be executed ignoring any exceptions.