all: Add receive only folder type (#5027)

Adds a receive only folder type that does not send changes, and where the user can optionally revert local changes. Also changes some of the icons to make the three folder types distinguishable.

lib/config/foldertype.go

@@ -11,6 +11,7 @@ type FolderType int
 const (
 	FolderTypeSendReceive FolderType = iota // default is sendreceive
 	FolderTypeSendOnly
+	FolderTypeReceiveOnly
 )
 
 func (t FolderType) String() string {
@@ -19,6 +20,8 @@ func (t FolderType) String() string {
 		return "sendreceive"
 	case FolderTypeSendOnly:
 		return "sendonly"
+	case FolderTypeReceiveOnly:
+		return "receiveonly"
 	default:
 		return "unknown"
 	}
@@ -34,6 +37,8 @@ func (t *FolderType) UnmarshalText(bs []byte) error {
 		*t = FolderTypeSendReceive
 	case "readonly", "sendonly":
 		*t = FolderTypeSendOnly
+	case "receiveonly":
+		*t = FolderTypeReceiveOnly
 	default:
 		*t = FolderTypeSendReceive
 	}