Zenodo integration

Making this upload files to Zenodo. Currently it's only uploading to the sandbox site while testing. Uploads look like this:

https://sandbox.zenodo.org/record/522627

Everyone (@openflexure) should add themselves to the contributors in metadata.yaml. Feel free to do that on this branch.

@rwb27, it currently only uploads the same as what's uploaded to build.openflexure.org, i.e. the STLs and docs. Do we want a zip for the OpenSCAD files too? The whole repository?

@jtc42 feel free to remove all the zenodo-test archives from https://build.openflexure.org/openflexure-microscope/ once this is merged.