Jnygaard depth buffer experimental

This branch adds an "autoProxy" mode for proxy geometry generation and rendering. There is a new example containing a small GUI for manipulating a few tunable parameters for this feature, see 'examples/auto_proxy_test'. (This is based on 'cuberenderer'.) The 'combined_unittest' runs without error. Tested in QtController mode, not trell. Also tested with an unmodified test job ('cuberenderer' and 'simplejob'.) To enable, simply add the boolean element 'useAutoProxy' to ExposedModel, with value 'true', e.g., like this:

    m_model->addElement<bool>( "useAutoProxy", true );