Use new framework support for depth-buffers to greatly simplify Simple Server, share updated drawing code including support for high resolution displays
- Simple Server: do away with an app FBO and draw directly into the SyphonServer, using its image for our local view and reducing the amount of work to be done per frame,
  which also fixes a long-standing issue with compositions which required a depth buffer.
- Simple Server: only draw or publish when the Quartz Composition has a changed frame
- Simple Server and Simple Client: share drawing code in a new view with support for high-resolution ("Retina") displays