chore: Make example/server usable for tests (#205)

* internal -> storage; split users into an interface

* move example/server/*.go to example/server/exampleop/

* export all User fields

* storage -> Storage

* example server now passes tests

example/server/internal/token.go

@@ -1,25 +0,0 @@
-package internal
-
-import "time"
-
-type Token struct {
-	ID             string
-	ApplicationID  string
-	Subject        string
-	RefreshTokenID string
-	Audience       []string
-	Expiration     time.Time
-	Scopes         []string
-}
-
-type RefreshToken struct {
-	ID            string
-	Token         string
-	AuthTime      time.Time
-	AMR           []string
-	Audience      []string
-	UserID        string
-	ApplicationID string
-	Expiration    time.Time
-	Scopes        []string
-}