Adex connector

Hi -- just added an implementation for the filtering.
Here's how I configure my client in the C++ bid_request_endpoint.cc
for (auto & c: agent.config.creatives) {
c.providerConfig["adx"]["externalId"] = "fashion.com/70_percent/728x90";
c.providerConfig["adx"]["htmlTemplate"] = ""; 
c.providerConfig["adx"]["clickThroughUrl"] = "";
c.providerConfig["adx"]["agencyId"] = 59;
c.providerConfig["adx"]["vendorType"] = "10 28";
c.providerConfig["adx"]["attribute"] = "7 40 94";
c.providerConfig["adx"]["sensitiveCategory"] = "19 10";
}