gui, lib/config, lib/model: Support auto-accepting folders (fixes #2299)

Also introduces a new Waiter interface for config changes and segments the
configuration GUI.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4551

cmd/syncthing/main.go

@@ -1080,14 +1080,7 @@ func defaultConfig(cfgFile string) *config.Wrapper {
 
 	if !noDefaultFolder {
 		l.Infoln("Default folder created and/or linked to new config")
-		defaultFolder = config.NewFolderConfiguration("default", fs.FilesystemTypeBasic, locations[locDefFolder])
-		defaultFolder.Label = "Default Folder"
-		defaultFolder.RescanIntervalS = 60
-		defaultFolder.FSWatcherDelayS = 10
-		defaultFolder.MinDiskFree = config.Size{Value: 1, Unit: "%"}
-		defaultFolder.Devices = []config.FolderDeviceConfiguration{{DeviceID: myID}}
-		defaultFolder.AutoNormalize = true
-		defaultFolder.MaxConflicts = -1
+		defaultFolder = config.NewFolderConfiguration(myID, "default", "Default Folder", fs.FilesystemTypeBasic, locations[locDefFolder])
 	} else {
 		l.Infoln("We will skip creation of a default folder on first start since the proper envvar is set")
 	}
@@ -1331,7 +1324,7 @@ func setPauseState(cfg *config.Wrapper, paused bool) {
 	for i := range raw.Folders {
 		raw.Folders[i].Paused = paused
 	}
-	if err := cfg.Replace(raw); err != nil {
+	if _, err := cfg.Replace(raw); err != nil {
 		l.Fatalln("Cannot adjust paused state:", err)
 	}
 }