ADEN-308 Remove wgAdDriverUseGpt
ADEN-308 Signature and tests change of AdProviderAdDriver2
ADEN-308 Separate ad provider for full GPT
ADEN-308 wg variable for new GPT zones (including slot name)
ADEN-308 WF variables added to DefaultSettings.php
ADEN-308 flushAds not to cause errors when gpt is not loaded
Merge pull request #1374 from Wikia/aden-308-full-gpt-with-unique-slot-names-2

ADEN-308 Full GPT with unique slot names configurable through wg variables