ENH: Added new graphFunctionObject function object

Accumulates function object result values and renders into a graph in SVG format

Minimal example by using system/controlDict.functions to plot the residuals from
the solverInfo function Object:

    residualGraph
    {
        type            graphFunctionObject;
        libs            (utilityFunctionObjects);
        writeControl    writeTime;

        logScaleX       no;
        logScaleY       yes;

        xlabel          "Iteration";
        ylabel          "log10(Initial residual)";

        functions
        {
            line1
            {
                object      solverInfo1;
                entry       Ux_initial;
            }
            line2
            {
                object      solverInfo1;
                entry       Uy_initial;
            }
            line3
            {
                object      solverInfo1;
                entry       Uz_initial;
            }
            line4
            {
                object      solverInfo1;
                entry       p_initial;
            }
        }
    }