Refactor state tracking (...)

Move state tracking into the puller/scanner objects. This is a first
step towards resolving #1391.

Rename Puller and Scanner to roFolder and rwFolder as they have more
duties than just pulling and scanning, and don't need to be exported.

internal/model/puller_test.go

@@ -72,7 +72,7 @@ func TestHandleFile(t *testing.T) {
 	// Update index
 	m.updateLocal("default", existingFile)
 
-	p := Puller{
+	p := rwFolder{
 		folder: "default",
 		dir:    "testdata",
 		model:  m,
@@ -126,7 +126,7 @@ func TestHandleFileWithTemp(t *testing.T) {
 	// Update index
 	m.updateLocal("default", existingFile)
 
-	p := Puller{
+	p := rwFolder{
 		folder: "default",
 		dir:    "testdata",
 		model:  m,
@@ -197,7 +197,7 @@ func TestCopierFinder(t *testing.T) {
 		}
 	}
 
-	p := Puller{
+	p := rwFolder{
 		folder: "default",
 		dir:    "testdata",
 		model:  m,
@@ -331,7 +331,7 @@ func TestLastResortPulling(t *testing.T) {
 		t.Error("Expected block not found")
 	}
 
-	p := Puller{
+	p := rwFolder{
 		folder: "default",
 		dir:    "testdata",
 		model:  m,
@@ -384,7 +384,7 @@ func TestDeregisterOnFailInCopy(t *testing.T) {
 	emitter := NewProgressEmitter(defaultConfig)
 	go emitter.Serve()
 
-	p := Puller{
+	p := rwFolder{
 		folder:          "default",
 		dir:             "testdata",
 		model:           m,
@@ -471,7 +471,7 @@ func TestDeregisterOnFailInPull(t *testing.T) {
 	emitter := NewProgressEmitter(defaultConfig)
 	go emitter.Serve()
 
-	p := Puller{
+	p := rwFolder{
 		folder:          "default",
 		dir:             "testdata",
 		model:           m,