Tests: Add test for the vtkCornerAnnotation class

Today's code based on the Wiki example:
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/CornerAnnotation

Plus a few mods to do an image regression test.

Change-Id: I9264c16ac03391e046ea047f5b4cda0d934a280a
Merge topic 'Coverage_CornerAnnotation' into master

4943d65b Tests: Add test for the vtkCornerAnnotation class