Schema API should switch to file backend

[cnrdh]

To avoid inconsistency issues, we switch /schema to a file system backed API.

There are 4 simple rules to follow

0. Naming convention is semantic like /schema/dataset-1.x.y[.dev].json (where x is major and y minor edit number)
1. Never update a file once published (increment version)
2. Copy (don't symlink) latest versioned file into a file without versioning
3. Always declare explicit versions on the client side
4. User same version in filename and in schema's id

[cnrdh]

Rule 0 Never use the .json in URIs (but do use them in filenames)

Rule 2 cp dataset-1.y.z.json dataset.json

Rule 4 This makes sure that even if the URI "http://api.npolar.no/schema/project" is used, the errors will state schema version "http://api.npolar.no/schema/project-1.x.z"

[cnrdh]

In production, using Rack::TryStatic https://github.com/npolar/api.npolar.no/commit/308161fcaa6b176fb6e1521c2ff8cea5df39997a