Passing assignmentID to Qualtrics

The R Package "MTurkR" offers a nice way to automate granting bonuses, but requires assignmentID as well as workerID as input. This modification adds "assignmentID" to surveyURL (if SEND_ID_TO_SURVEY is set to true).

I also renamed "workerId" to "workerID" in the surveyURL, which seems more intuitive.