Ghostery changes for Offers support

[zarembsky]

• [x ] Have you followed the guidelines in CONTRIBUTING.md?
• [x ] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x ] Have you added an explanation of what your changes do?
• [x ] Does your submission pass tests?
• [x ] Did you lint your code prior to submission?

[agustin-cliqz]

Hi Serge, looks good, regarding the CliqzEvents interface (to subscribe to events), lets ask @chrmod if he thinks there will be any problems with it (I can implement the interface should be trivial)