To avoid a error window from VTK due to the txtactor having no scalars.
Merge pull request #823 from larshg/FixNoScalarValues

To avoid a error window from VTK (6) due to the txtactor having no scalars.
Move visualization doc from overview to tutorials and remove overview dir
Move generation of advanced doc into own CMakeLists.txt

- Move find_package(Sphinx) into doc/CMakeLists.txt.
- Move Sphinx doctrees into build dir.
- Remove old Makefiles.
Rename ihs_lion_photo.JPG ihs_lion_photo.jpg
Only remove share/doc if WITH_DOCS is set.

- move WITH_DOCS to pcl_options.cmake.