bugfix - fixed a small bug in the finding of min and max plot values,
where if only one was null, both would be reset from data.
init - also added a test icon.
init - added pictograms for use in the QFTSandbox.
removed - removed some investigation files (error plots).
improved - changed the integrators and Hamiltonians to support multiple
interactions simultaneously.
removed - removed some of the unused integrators (States).
moved - put all the icons into their own package (to clean up). Updated
the path in the sandbox to reflect this.