Update build for Py3 and Gst 1.0
Changes
This MR updates the build files to work with updated dependencies.
This repeats all changes from !226 (closed) for these files.
Purpose
I intend to split !226 (closed)'s changes into a number of MRs, which won't be functional code versions themselves, but once complete will encompass the full set of changes to upgrade to py3.
This should provide useful code diffs for reviewers.