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

tests/integration/test_sync_window.gd

@@ -143,3 +143,13 @@ func test_reopening_after_sync_shows_result_without_syncing_again() -> void:
 
     assert_int(_server.count("/sync")).is_equal(1)
     assert_str(_node("SyncTitleLabel").text).is_equal("Sync Result")
+
+
+func test_errors_section_has_errors_header() -> void:
+    _runner.invoke("start_sync")
+    var result: Dictionary = _empty_result()
+    result.catched_errors = ["Could not read tags in broken.mp3"]
+
+    _finish_sync(result)
+
+    assert_str((_node("CatchedErrorsVBox").get_child(0) as Label).text).is_equal("Errors")