Add URL box to where rappmgr.cab is stored

I propose a URL box should be implemented in the settings dialog of RAPPS that could be changed by the user. The default text would need to be http://svn.reactos.org/packages/rappmgr.cab. This would be useful so users could practice writing the text files needed without having to send it off. I know the URL of the cab can be changed in rapps.h but it would simplify the process of editing and compiling especially if some people don't know how to compile ReactOS (I would hope they know how to compile ReactOS).