Switching to experimental brushes and back shouldn't require a restart

[andybak]

#620 and #573 removes most uses of experimental mode - so the setting now basically just about the brush manifest.

I tried this:

    public void SetIsExperimental(bool active)
    {
        PlayerPrefs.SetInt("ExperimentalMode", active ? 1 : 0);
        BrushCatalog.m_Instance.Init();
        BrushCatalog.m_Instance.BeginReload();
    }

(where Init() is the previous Awake() moved into a separate method) but it's not working for some reason.