ENH: GUI problems on MacOS, xml info

-The GUI now appears on top of Slicer when FiberViewerLight is started as a Slicer extension on MacOS
-Some buttons appeared to small on MacOS (at least on small screens). The maximum size of the qt group including those buttons has been increased
-A version number, an acknowledgment as well as a link to the documentation page on the Slicer wiki have been added to the xml description file

diff: http://www.nitrc.org/plugins/scmsvn/viewcvs.php?view=rev&root=fvlight&revision=61
Merge pull request #412 from fbudin69500/update-FiberViewerLight

ENH: GUI problems on MacOS, xml info