Tweaked def Computed tomography; made second level methods disjoint
More descriptive OBOF ulabels added. This time for methods to enhance constrast.  Also flattened the graph further - shifting up classes under light microscopy, such as <contrast-enhancing method> and <source of contrast> all the way to the top. Need to check thiat this is not problematic for cell image library - @wawong - can you check? - May be some cases where these classes should still have some relationship to light microscopy, as probably significant proportion  only used there.
Merge branch 'master' of https://github.com/dosumis/fbbi