Adds support for UTF-8 bid requests.

Change the bidRequestStr in SubmittedAuctionEvent, SubmissionInfo
and FinishedInfo from std::string to Datacratic::Utf8String.
This fixes an issue where the router would throw and exception
stating "Invalid character in JSON string" if the bid request
had non-ascii characters.
Merge pull request #106 from USMediaConsulting/utf8-request

Adds support for UTF-8 bid requests.