- MainWindow: add second codepath to drive the rendering using a Windows.Forms.Timer instead of AppIdle. On the machines I've tested so far, this does not seem to be an improvement, so it is off by default.
- MainWindow: add second codepath to drive the rendering using a Windows.Forms.Timer instead of AppIdle. On the machines I've tested so far, this does not seem to be an improvement, so it is off by default.

dayo7116/open3mod,acgessler/open3mod,acgessler/open3mod,zhukaixy/open3mod,dayo7116/open3mod,zhukaixy/open3mod