ENH: Move classes into itk::tube namespace and rename .txx files

Change-Id: Ibb1ddb811ff6fd989f1e5f42307d2c57e129de53
Merge topic 'AddToItkTubeNamespace'

0588958 ENH: Move classes into itk::tube namespace and rename .txx files
ENH: Add markdown formatted README and LICENSE and update acknowledgements

Acknowledgements have also been updated in NIH format

http://grants.nih.gov/grants/acknow.htm

using the list on public wiki

http://public.kitware.com/Wiki/TubeTK/About

Change-Id: I191c3da0c0047a1cabd90640b5295e748843b5f1