Low order tasks

* Added all tutorials
* Updated documentation
* Deleted unnecessary files
* Fixed an important bug in VizAccessor
* Hide add/remove methods in VizAccessor
* Text3DWidget provides the option for deciding if the text should face the camera
* Added license headers
* CameraPositionWidget has a new constructor for showing image using field of view
* VTK 6.0.0 support is provided
* TODO: CMakeList needs to be checked, I made the following:

```
find_package(VTK 5.10.0)
if (NOT VTK_FOUND)
   find_package(VTK 6.0.0)
```
   This way, if 5.10 is found, I use that one, if not, I check 6.0. If it doesn't exist, we have the fatal error.