ENH: Clean up CLIs and library exporting

This allows projects outside of TubeTK to easily build each of TubeTK's
application or module. It also improves linking against TubeTK's libraries.
ENH: Move TubeTKConfig.cmake to superbuild directory

Much like CTK, it is easier for other projects building TubeTK to look for
the TubeTKConfig.cmake in the superbuild directory instead of its inner build.
UseTubeTK.cmake and TubeTKTargets.cmake have been moved along as well.
ENH: Delete FindTubeTK.cmake

Find*.cmake should only be written to handle project's specific
configurations issues. Since TubeTK doesn't have any, the regular
find_package should be able to do its job without a FindTubeTK.cmake.