Tidy up popup layouts

- Settings: labels in one column and switches and number buttons lined
  up in another, with margins inside the panel
- Log: title and margins; text no longer touches the panel edge
- Sync result: error list centred under its header, which now reads
  Errors instead of CatchedErrors
- About: text wraps inside the panel instead of running under the
  scrollbar
- Character select: wider panel, so the right column of characters is
  no longer right next to the scrollbar

MainWindow.tscn

@@ -411,9 +411,9 @@ offset_bottom = 153.0
 unique_name_in_owner = true
 visible = false
 layout_mode = 1
-offset_left = 420.0
+offset_left = 405.0
 offset_top = 165.0
-offset_right = 1572.0
+offset_right = 1557.0
 offset_bottom = 805.0
 
 [node name="ShortcutsWindow" parent="." unique_id=1513416242 instance=ExtResource("13_8eebo")]