RTBKitExchangeConnector now populates the externalId in the BidResponse
per Bid
HttpBidderInterface now sends only one HTTP request and uses the Bid
extension field to lookup the correct agent and AgentConfig

Conflicts:

	rtbkit/plugins/bidder_interface/http_bidder_interface.cc
externalId is now populated as an unsigned int rather than a string in
RTBKitExchangeConnector
bidder_test now setups the correct stacks with correct exchange connectors
Merge pull request #55 from datacratic/http_bidder_interface_tweaks

Http Bidder Interface
rtbkit_integration_test: make use of a configurable number of agents
"toPopupTransfer" -> "topupTransfer" and reworked indentation
rtbkit_integration_test: cleanup of the code handling multiple agents/accounts
rtbkit_integration_test: improved support for HTTP application layer
slave banker: added some metrics for the account sync
slave_banker: removed comments
rtbkit_integration_test: use static_pointer_cast<T> when casting a Banker to a SlaveBanker
rtbkit_integration_test: use ZMQ_APP_LAYER, since it fits the first scope of the test and enables it to pass
rtbkit_integration_test: reduced number of accounts to 50, to lower pressure on our test machine
bidder_interface.mk: added dependency of librtb on bidder_interface plugins
Merge branch 'master' into http-application-layer-benchmarks

Conflicts:
	rtbkit/examples/rtbkit_integration_test.cc