Allow enable/disable of tweak without respring

[conath]

Currently the isTweakEnabled gets checked in CCUIControlCenterViewController _loadPages:

- (void)_loadPages {
  LoadPrefs();
  if (!isTweakEnabled) {
    %orig;
    return;
  }
// else load tweak into CC …

This requires a respring to be called again (according to brief testing).