Add a lock between all git operations

This way in between a git add + git commit, no other git operation will
run. This rarely occurs but it was a posibility depending on the speed
of the users actions.

lib/state_container.dart

@@ -14,10 +14,13 @@ import 'package:gitjournal/settings.dart';
 import 'package:path/path.dart' as p;
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:flutter_crashlytics/flutter_crashlytics.dart';
+import 'package:synchronized/synchronized.dart';
 
 class StateContainer with ChangeNotifier {
   final AppState appState;
 
+  final _opLock = Lock();
+
   // FIXME: The gitRepo should never be changed once it has been setup
   //        We should always just be modifying the 'git remotes'
   //        With that, the StateContainer can be a StatelessWidget
@@ -118,6 +121,7 @@ class StateContainer with ChangeNotifier {
   }
 
   void createFolder(NotesFolderFS parent, String folderName) async {
+    return _opLock.synchronized(() async {
       var newFolderPath = p.join(parent.folderPath, folderName);
       var newFolder = NotesFolderFS(parent, newFolderPath);
       newFolder.create();
@@ -128,18 +132,22 @@ class StateContainer with ChangeNotifier {
       _gitRepo.addFolder(newFolder).then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void removeFolder(NotesFolderFS folder) {
+  void removeFolder(NotesFolderFS folder) async {
+    return _opLock.synchronized(() async {
       Fimber.d("Removing Folder: " + folder.folderPath);
 
       folder.parentFS.removeFolder(folder);
       _gitRepo.removeFolder(folder.folderPath).then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void renameFolder(NotesFolderFS folder, String newFolderName) {
+  void renameFolder(NotesFolderFS folder, String newFolderName) async {
+    return _opLock.synchronized(() async {
       var oldFolderPath = folder.folderPath;
       folder.rename(newFolderName);
 
@@ -148,39 +156,47 @@ class StateContainer with ChangeNotifier {
           .then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void renameNote(Note note, String newFileName) {
+  void renameNote(Note note, String newFileName) async {
+    return _opLock.synchronized(() async {
       var oldNotePath = note.filePath;
       note.rename(newFileName);
 
       _gitRepo.renameNote(oldNotePath, note.filePath).then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void moveNote(Note note, NotesFolderFS destFolder) {
+  void moveNote(Note note, NotesFolderFS destFolder) async {
     if (destFolder.folderPath == note.parent.folderPath) {
       return;
     }
+    return _opLock.synchronized(() async {
       var oldNotePath = note.filePath;
       note.move(destFolder);
 
       _gitRepo.moveNote(oldNotePath, note.filePath).then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void addNote(Note note) {
+  void addNote(Note note) async {
+    return _opLock.synchronized(() async {
       Fimber.d("State Container addNote");
       note.parent.insert(0, note);
       note.updateModified();
       _gitRepo.addNote(note).then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void removeNote(Note note) {
+  void removeNote(Note note) async {
+    return _opLock.synchronized(() async {
       // FIXME: What if the Note hasn't yet been saved?
       note.parent.remove(note);
       _gitRepo.removeNote(note.filePath).then((NoteRepoResult _) async {
@@ -191,21 +207,26 @@ class StateContainer with ChangeNotifier {
         await Future.delayed(const Duration(seconds: 4));
         _syncNotes();
       });
+    });
   }
 
-  void undoRemoveNote(Note note) {
+  void undoRemoveNote(Note note) async {
+    return _opLock.synchronized(() async {
       note.parent.insert(0, note);
       _gitRepo.resetLastCommit().then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
-  void updateNote(Note note) {
+  void updateNote(Note note) async {
+    return _opLock.synchronized(() async {
       Fimber.d("State Container updateNote");
       note.updateModified();
       _gitRepo.updateNote(note).then((NoteRepoResult _) {
         _syncNotes();
       });
+    });
   }
 
   void completeGitHostSetup() {