Settings: Move Editor Settings to their own screen

It just has the default settings right now, but we need to expose some
settings in the Markdown Editor.

lib/screens/settings_editors.dart

@@ -0,0 +1,46 @@
+import 'package:flutter/material.dart';
+import 'package:gitjournal/settings.dart';
+import 'package:gitjournal/screens/settings_widgets.dart';
+
+class SettingsEditorsScreen extends StatefulWidget {
+  @override
+  SettingsEditorsScreenState createState() => SettingsEditorsScreenState();
+}
+
+class SettingsEditorsScreenState extends State<SettingsEditorsScreen> {
+  @override
+  Widget build(BuildContext context) {
+    var settings = Settings.instance;
+
+    var body = Column(children: <Widget>[
+      ListPreference(
+        title: "Default Editor",
+        currentOption: settings.defaultEditor.toPublicString(),
+        options:
+            SettingsEditorType.options.map((f) => f.toPublicString()).toList(),
+        onChange: (String publicStr) {
+          var val = SettingsEditorType.fromPublicString(publicStr);
+          Settings.instance.defaultEditor = val;
+          Settings.instance.save();
+          setState(() {});
+        },
+      ),
+    ]);
+
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Editor Settings'),
+        leading: IconButton(
+          icon: const Icon(Icons.arrow_back),
+          onPressed: () {
+            Navigator.of(context).pop();
+          },
+        ),
+      ),
+      body: Padding(
+        padding: const EdgeInsets.all(16.0),
+        child: body,
+      ),
+    );
+  }
+}

lib/screens/settings_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:gitjournal/core/notes_folder_fs.dart';
+import 'package:gitjournal/screens/settings_editors.dart';
 import 'package:gitjournal/settings.dart';
 import 'package:gitjournal/state_container.dart';
 import 'package:gitjournal/utils.dart';
@@ -168,17 +169,14 @@ class SettingsListState extends State<SettingsList> {
         enabled: remoteGitConfigured,
       ),
       const SizedBox(height: 16.0),
-      SettingsHeader("Editor Settings"),
-      ListPreference(
-        title: "Default Editor",
-        currentOption: settings.defaultEditor.toPublicString(),
-        options:
-            SettingsEditorType.options.map((f) => f.toPublicString()).toList(),
-        onChange: (String publicStr) {
-          var val = SettingsEditorType.fromPublicString(publicStr);
-          Settings.instance.defaultEditor = val;
-          Settings.instance.save();
-          setState(() {});
+      ListTile(
+        title: const Text("Editor Settings"),
+        subtitle: const Text("Configure how different editors work"),
+        onTap: () {
+          var route = MaterialPageRoute(
+            builder: (context) => SettingsEditorsScreen(),
+          );
+          Navigator.of(context).push(route);
         },
       ),
       SettingsHeader("Storage"),