Split settings into a quiz card and an application Settings popup

- A Quiz settings button under the player bar opens a small card above
  it with the quiz settings, including Auto repeat, which moves there
  from under the player bar. The card does not dim the quiz, so it can
  be changed during a song, and grows to fit its rows.
- A Settings button in the top bar opens the application settings:
  server, fullscreen and songs to download ahead. Quick sync is gone,
  as the server no longer has it, and the server list is in Settings.
- Labels use sentence case, and seconds to hide show as whole numbers.
- Debug builds switch to the local server and a low winning score in
  the Settings autoload, before any scene asks the server for anything.
  The DEBUG label moves to the top bar, so it shows on every tab.
- Search moves from the top bar back to the quiz toolbar, as the
  Statistics tab has its own search.

tests/integration/test_popups.gd

@@ -6,11 +6,12 @@ extends MainWindowTestSuite
 ## Popups in the main window: the ones opened from the top bar, and the log.
 const MAIN_POPUPS: Array[String] = [
 	"SearchPopup", "SyncPopup", "QRPopup", "ShortcutsPopup", "AboutPopup", "LogPopup",
+	"SettingsPopup",
 ]
 
 ## Popups opened from the quiz, in the Quiz scene.
 const QUIZ_POPUPS: Array[String] = [
-	"SettingsPopup", "CharacterSelectPopup", "WinnerPopup",
+	"CharacterSelectPopup", "WinnerPopup",
 ]
 
 
@@ -20,7 +21,7 @@ func _popup(node_name: String) -> BasePopup:
 
 
 ## The backdrop that shows behind [param popup].
-func _backdrop(popup: BasePopup = _popup("SettingsPopup")) -> ColorRect:
+func _backdrop(popup: BasePopup = _popup("CharacterSelectPopup")) -> ColorRect:
 	return popup.get_parent().get_node("PopupBackdrop")
 
 
@@ -32,12 +33,12 @@ func _outside(popup: BasePopup) -> Vector2:
 
 
 func test_backdrops_are_hidden_without_popups() -> void:
-	assert_bool(_backdrop(_popup("SettingsPopup")).visible).is_false()
+	assert_bool(_backdrop(_popup("CharacterSelectPopup")).visible).is_false()
 	assert_bool(_backdrop(_popup("AboutPopup")).visible).is_false()
 
 
 func test_backdrops_cover_the_whole_window() -> void:
-	for node_name: String in ["SettingsPopup", "AboutPopup"]:
+	for node_name: String in ["CharacterSelectPopup", "AboutPopup"]:
 		var popup: BasePopup = _popup(node_name)
 		popup.open()