Integrate Yiwen's materials database look-up with PDT GUI
Yiwen has a Tk/Tcl-based GUI that looks up material properties based on wavelengths and tissue types. This should be integrated as a "look up" button in the optical properties specification dialog so users can click on a material and have the data populated in the optical properties dialog.
Directly entering (typing) in optical properties should also still work (i.e. this is an enhancement).