more improvements to xrf display
add periodic table to select K,L,M markers for fluorescence lines
added perioic table to xrf_display... more work needed
periodic table widget complete
added .add_roi() method to medfile group
added add_checkbox to wxutils
xrfdisplay: many changes, improvement, configurations
improvements to plot_arrow
more improvements to xrf display
postpone using plot(..,delay_draw=True)