GitLab

I was going through policy stuff here:

https://www.mediawiki.org/wiki/GitLab/Policy#Permissions

...and noticed we'd written this:

> The "Pipelines" setting in public namespaced projects should be
> set to "Only Project Members". This ensures that only project
> members with Reporter privileges are able to run tests on a
> particular project.

I believe that's what's now under Project -> Settings -> Visibility,
project features, permissions -> CI/CD.  I'm not _totally_ sure what
effect this has, so I guess we'll need to experiment here, and may want
to make it optional on a per-project basis.

This also makes the project settings updates only do a single write per
changed project.

The project configuration stuff should be rolled into the `settings` CLI
elsewhere in this repo, but I'll save that for a later MR.

`configure-projects` uses the python-gitlab project to loop over all
projects in the instance and disable issues and wikis.

This also adds a requirements.txt and some rudimentary instructions in the
README.