No sync on startup; new command import contacts

Having an import of all contacts on each startup and after login is very
annoying, if you have a big list of contacts. If you choose to not join a
room with all contacts, you get the invitation over and over on each
restart of the service. Better is to have a command for the management
room to explicitly start the import.

main.go

@@ -185,7 +185,7 @@ func (bridge *Bridge) UpdateBotProfile() {
 
 func (bridge *Bridge) StartUsers() {
 	for _, user := range bridge.GetAllUsers() {
-		go user.Start()
+		go user.Connect(false)
 	}
 }