First steps to move away from cucumber

Summary:
Extracted the ZanshinContext class and ported the cucumber regexp to
regular methods. Added a bit of syntactic sugar for using the API. Also
ported a couple of feature files to become regular Qt automated tests.
Looking good so far.

More ports are needed... just saying... ;-)

Reviewers: bensi, dfaure

Differential Revision: https://phabricator.kde.org/D18209