move to FFG System Toolbox

[ghost]

This toolbox will become a (custom) System Toolbox, like the DSP System Toolbox or the Communication System Toolbox. Let's call our toolbox the FFG System Toolbox, where FFG is short for Forney-style Factor Graph.

Let's also take over MATLAB's conventions for System Toolboxes. For instance, I create an audio player object by

>> x = dsp.AudioPlayer( 'SampleRate', 16000 );

I think we should do a similar convention, as in:

>> xin = ffg.EvidenceNode( 'id', 1 );

instead of

>> xin = evidencenode(1); 

I.o.w.:

1. move stuff to the FFG Package
2. Methods in UpperCamelCase
3. Use property-value pairs for setting properties (have a look at this: http://www.mathworks.com/matlabcentral/fileexchange/22671-parse-propertyvalue-pairs-and-structures)