Add basic legacy login

Add initial setup/context and first login feature to login to administration interface
Thought this was documented, I'll add a PR to cover this.

But the idea is to have the scenarios with case insensitive to be easier to write the scenarios.
However in the identifier map it is needed to be in lower case since the match will be with `strtolower` (see [BehatBundle/Context/BrowserContext.php#107](https://github.com/ezsystems/BehatBundle/blob/master/Context/BrowserContext.php#L107))