Consistent way to refer to ITK classes, namespaces, and ITK in Doxygen

[jhlegarreta]

Description

Doxygen automatically links to documented classes:

All words in the documentation that correspond to a documented class and contain at least one non-lower case character
will automatically be replaced by a link to the page containing the documentation of the class. 

Some classes mention other ITK classes as fully qualified names, e.g. itk::Image, e.g.
https://itk.org/Doxygen/html/classitk_1_1ImageToVTKImageFilter.html

whereas other simply use Image, e.g.
https://itk.org/Doxygen/html/classitk_1_1CovariantVector.html

Additionally, decide whether the case used for ITK will be lowercase (itk) or uppercase (ITK). Note that neither gets linked to the itk namespace by Doxygen. Maybe there is a way to do it: maybe using the \ref command:
"To link to an all lower case symbol, use \ref."

It should be decided in which cases we will be willing to link to the ITK namespace. The can apply to other namespaces.

The decisions should be documented in the ITK Software Guide.

Expected information

Consistent way to refer to ITK classes, namespaces, and ITK itself.

Actual information

Inconsistent way to refer to ITK classes,, namespaces, and ITK itself.

Versions

master

Additional Information

None.