Separate graph code and data

[jteresco]

The graph data should be in a separate directory from graphs/index.php since the new site update process re-creates the directory with data each time.

[jteresco]

TravelMapping/Web#255 has been created to indicate changes needed to graphs/index.php when this change is made.

[jteresco]

I believe this is now complete. Please open new issues if there are problems.