Inconsistent links to pre- and post- instructor training surveys

[anenadic]

Inconsistent links to pre- and post-instructor-training survey are being used (see https://gcapes.github.io/2019-10-08-ttt-manchester/ for example):

• pre-workshop survey link is https://www.surveymonkey.com/r/instructor_training_pre_survey?workshop_id=2019-10-08-ttt-manchester and points to the survey in Survey Monkey
• post-workshop link points to the page in instructor training material about surveys https://carpentries.github.io/instructor-training/06-feedback/#surveys where we do not have links to post instructor training surveys at all