Scrap dangerous and hard to support features

[MrBunsy]

Up for some discussion, but I see no reason to keep the following:

• Manage Metadata Fields. I can see no reason you'd ever want to add a field via the web GUI. You can't really make use of it without editing a lot of other things (citations, actual code, templates, workflows, rendering)
• View config. If we had a "real" configuration system that actually presented all fields all plugins required configuring (ala Jenkins). I'd understand this. Instead we've given admins enough rope to shoot themselves.

And I think it's worth considering scrapping these, but am open to persuasion:

• Reload Config. I didn't think there was any time this was ever needed, but with "Phrase saved. Full configuration reload not required." is not true #360 I can see there are some still.
• Indexer controls. I'm of the view that we should only support a robust systemd service for the indexer.

Any features we support need testing, and need customers supporting. The fewer the features, the less work!