Use Qt4 by default instead of Qt5

Earlier version of VTK does not support Qt5 and PCL will not compile
correctly when Qt5 is used by default.
From VTK wiki (http://www.vtk.org/Wiki/VTK/Configure_and_Build):
```
Building VTK with Qt is a common use case for the creation of nice
user interfaces. Using Qt 4.8.* is recommended, but earlier versions
and Qt 5.* are in various stages of support.
...
Qt5.*
Warning: This has only been tested on Qt5.2.1, and only on a few systems.
```
Add Glasbey color mapping mode in PointCloudImageExtractorFromLabelField

The Glasbey lookup table (LUT) is a color table structured in a
maximally discontinuous manner. That is, adjacent color bins are chosen
to be as distinct from one another as possible.
Update pcl_pcd2png tool to support Glasbey color mode
Add a protected virtual method extractImpl() in image extractors
Add a missing template specialization for isFinite<Intensity>()
Add a option to paint infinte points with black
Update pcl_pcd2png tool to support painting infinite points with black
Fixed getColor method for HSV to RGB conversion

Within the method getColor for HSV colored points the following issues
have been fixed:
- conversion from HSV to RGB values
- faulty return lines
- behaviour for H values > 360 and < 0, so that the color
  gradient is continuous.

The following things have been added:
- limited s and v to [0.0,1.0], that values < 0.0 are set to 0.0 and
  values > 1.0 are set to 1.0.
Solving a linker error with median_filter.cpp

Solving a linker error with point type XYZI which is not pre-compiled for this filter. The solution that worked was to include the #include <pcl/filters/impl/median_filter.hpp> A better solution is to change the source file to instantiate common point types.
Merge pull request #773 from sidahuja/patch-1

Solving a linker error with median_filter.cpp
Merge pull request #767 from taketwo/update-pcd2png

Update PointCloudImageExtractors and pcd2png tool
Merge pull request #772 from jgarstka/color_handler_fix

Fixed getColor method for HSV to RGB conversion
Merge pull request #765 from xiangxw/qt4_default

Use Qt4 by default instead of Qt5