Chart risk v cost of project options

[BlairMoir]

Add a chart to plot risk v cost v duration of multiple project options.

I see two obvious routes to implementation

1. Leave the main program as it is, have the chart read the metrics for all the files in the current directory. With an option for the user to toggle which ones to include on the chart page .
2. Allow the user to edit multiple files concurrently

[LarsKemmann]

Critical Pass has a concept of a "tree" of projects where the user can create revisions of a project plan and track the relationship between those revisions. Route 1 above feels like a relatively (?) straightforward way to reach a similar result... it probably needs a "Plan Versions" panel that lists all the plan files in the directory and lets the user switch between them quickly, and then the calculations need to be run for each version. Ideally, I could hide and show versions from the "Plan Versions" panel.