Added renderThread based on Runnable Renderer

Added renderThread based on Runnable Renderer
Started AWT renderer
Started renderThread
Moved relevant variables closer to run method
Added Javadoc comments to many variables
Modified thread monitoring and shutdown loop to
a timed join on the render thread with termination
based on the termination of the fo thread
public void setRenderer(String) changed to
public Renderer getRenderer(String)

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/branches/FOP_0-20-0_Alt-Design@197509 13f79535-47bb-0310-9956-ffa450edef68