In tests fetching plot detail, specify `instance` argument to `make_request`

I updated some of the plumbing which creates the context dict for plots to use `request.instance` rather than passing `instance` separately. So tests which constructed their own requests were breaking.
Do display "new point marker" for first marker in list (since polygon is closed)
Merge pull request #1283 from RickMohr/fix-django-tests

In tests fetching plot detail, pass `instance` argument to `make_request`