Added better Tenanting

* Removed Tenanting from base objects as some models may be tenantless
* Admins are naturally not restricted by tenants
* Users *ARE* the tenants (for now) so they don't require a tenant ID
either
* User-owned models should all include the Tenanted model as their base
* Created .Create and .Save methods attached to base model

models/tenanted.go

@@ -0,0 +1,21 @@
+package models
+
+import (
+	"errors"
+
+	"github.com/google/uuid"
+
+	"gorm.io/gorm"
+)
+
+type Tenanted struct {
+	Base
+	Tenant uuid.UUID `gorm:"index;<-:create"`
+}
+
+func (t *Tenanted) BeforeCreate(scope *gorm.DB) error {
+	if t.Tenant == uuid.Nil {
+		return errors.New("cannot save an untenanted object")
+	}
+	return nil
+}