add Logout, OnLogout to server manager and hook up OnLogout callbacks

backend/servermanager.go

@@ -13,6 +13,7 @@ type ServerManager struct {
 	Server   *subsonic.Client
 
 	onServerConnected []func()
+	onLogout          []func()
 }
 
 func NewServerManager() *ServerManager {
@@ -37,10 +38,25 @@ func (s *ServerManager) ConnectToServer(conf *ServerConfig, password string) err
 	return nil
 }
 
+func (s *ServerManager) Logout() {
+	if s.Server != nil {
+		keyring.Delete(AppName, s.ServerID.String())
+		for _, cb := range s.onLogout {
+			cb()
+		}
+		s.Server = nil
+		s.ServerID = uuid.UUID{}
+	}
+}
+
 func (s *ServerManager) OnServerConnected(cb func()) {
 	s.onServerConnected = append(s.onServerConnected, cb)
 }
 
+func (s *ServerManager) OnLogout(cb func()) {
+	s.onLogout = append(s.onLogout, cb)
+}
+
 func (s *ServerManager) GetServerPassword(server *ServerConfig) (string, error) {
 	return keyring.Get(AppName, server.ID.String())
 }