ui: (auto)save schema drafts in admin editor

[miguelgrc]

Saving changes to a schema requires bumping the version in the settings every time, which is not very comfortable. It would be nice to allow "draft" schema saves to DB, so that you can always keep the latest changes saved easily while you are working on a new version of your schema without needing to actually save a new version.

Should be done after cern-sis/react-formule#84