Pass capabilites to principal path handler

The capabilities are added automatically by the default principal path
handlers in the `caldav` and `carddav` packages. However, using the
custom handler, they have to be passed in manually.

These being missing before was a violation of the RFC and the cause for
issues when using e.g. DavX5 client. This is now fixed.

cmd/tokidoki/main.go

@@ -70,6 +70,10 @@ func (u *tokidokiHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		opts := webdav.ServePrincipalOptions{
 			CurrentUserPrincipalPath: userPrincipalPath,
 			HomeSets:                 homeSets,
+			Capabilities: []webdav.Capability{
+				carddav.CapabilityAddressBook,
+				caldav.CapabilityCalendar,
+			},
 		}
 
 		webdav.ServePrincipal(w, r, &opts)