Enable open authoring and editorial workflow

[timwis]

Per #210, this pull request enables open authoring, a beta feature that ships with Decap CMS (formerly Netlify CMS). It allows guests of the site to propose changes to its content via GitHub pull request, which I reckon would be quite a hit for an open data portal (especially if we add an "Add Dataset" button).

Here's what it looks like for a guest to propose an edit to a dataset (note they already have a GitHub account in this video, which presumably won't be the case for most guests):

open-authoring-guest.mov

At the end of this video, Decap CMS created a pull request on the site's repo. And, because it's hosted on Netlify with deploy previews, it also generated a preview site for the pull request.

The open authoring feature requires we enable another feature called "editorial workflow." In editorial workflow, changes (by normal admin users) are also proposed via pull request, in theory so that an editor can 'review' them. Decap CMS provides a kanban-style view for reviewing pull requests:

This is a nice feature if there are multiple people working on the site, though I imagine it's designed for reviewing prose (e.g. blog posts) rather than metadata, and the downside is that it takes several extra clicks and is less counter-intuitive to make a small change. Here's what the process looks like for an admin updating their own dataset:

open-authoring-normal-editing.mov

I'm leaving this as a draft pull request because I'd like feedback on whether we should enable this feature by default (well, technically both features), or have it be opt-in and document it? Perhaps we could trial it on OpenDataPhilly @BryanQuigley?

[BryanQuigley]

That looks awesome!

At the time being https://opendataphilly.org/ launched late last week with JKAN via GitHub Pages. (I also just left E84/Azavea, but still plan to be involved). We opted to get the launch done just to drop the Netlify Edit buttons.

I don't see any reason not to enable it for those that go the Netlify route (which I expect to be whoever does it next..).