Extract and interface for ExceptionHelper in package net.sf.openrocket.startup. ...

Extract and interface for ExceptionHelper in package net.sf.openrocket.startup.  Register an instance implementing this interface in the Application object in Startup2.  Use the static locator functions in Application to retrieve reference to the ExceptionHandler in all the dependent classes.  Note: net.sf.openrocket.gui.main.ExceptionHandler was renamed to net.sf.openrocket.gui.main.SwingExceptionHandler and all its static methods were changed to instance methods.

git-svn-id: https://openrocket.svn.sourceforge.net/svnroot/openrocket/trunk@237 180e2498-e6e9-4542-8430-84ac67f01cd8