Add DOFMap output class

As described in #4155 this output module dumps the degrees-of-freedom map in JSON format to a file and/or the screen. JSON is a widely supported text based serialization format. 

Besides the raw DOF data I'm also outputting active kernels for every subdomain (names and type names!). 


> On Nov 10, 2014, at 11:08 AM, Daniel Schwen <notifications@github.com> wrote:
> 
> In framework/src/outputs/DOFMapOutput.C:
> 
> > +  // If file output is desired, wipe out the existing file if not recovering
> > +  if (!_app.isRecovering())
> > +    writeStreamToFile(false);
> > +
> > +  // Output the system information
> > +  if (_system_information && _allow_output)
> > +    outputSystemInformation();
> > +}
> > +
> > +std::string
> > +DOFMapOutput::filename()
> > +{
> > +  return _file_base + ".json";
> > +}
> > +
> > +std::string
> My demangle implementation has a fallback that removes leading digits (which can never be parts of a valid class name).
> 
I think the demangler will still work if you remove this prefix yourself ahead of time.