feat: switch to SQL revocation database for revocation server, and to simple in-memory database for requestors

Requestors only need to be aware of the last x revocation records and none of the other record types.

Addionally:
- pass revocation configuration into RevocationStorage
- refactor irma.NewConfiguration functions to use options struct
- split RevocationStorage helper functions into separate structs
- add credentialtype to revocation record wrapper in irmago

feat: support revocation sessions in IRMA server, and move revocation code from irmaconfig.go to its own file