oauth2server: scopes registry
- Adds registry for OAuth 2.0 scopes.
- Adds support for selecting scopes when creating personal access tokens.
- Fixes scopes registration in deposit and webhooks modules according to new registry.
- NOTE The scopes registry will be refactored in the future depending on the outcome RFC #1773.
Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>