Implemented paging for gerrit data retrieval

Partially implements blueprint review-stats

Change-Id: I98e3f5459d19648597968d05999e1771a6e462ef
Use GitHub lib to retrieve project list

* Project list is retrieved with help of PyGitHub
* Difference in default data is checked by hash
* Fixed issue with invalid utf8 chars in git parsing

Partially implements blueprint add-more-projects.

Change-Id: I7cc9bc758c1f0d522af403a2b41c8298d80d843c