Fix compilation error related to GUI

[rolalaro]

• Added a vpDisplayFactory namespace that permits to either get a newly allocated vpDisplay* if a GUI library is available or a nullptr otherwise. It permits to check only VISP_HAVE_DISPLAY instead of several macro in a software to get a new display.
• Fix compilation errors when no GUI library is available

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 74 lines in your changes are missing coverage. Please review.

Project coverage is 45.84%. Comparing base (632b536) to head (41d8d3b).
Report is 6 commits behind head on master.

Files	Patch %	Lines
...l/robot/mbot/raspberry/visp/mbot-apriltag-ibvs.cpp	0.00%	14 Missing ⚠️
...l/robot/mbot/raspberry/visp/mbot-apriltag-pbvs.cpp	0.00%	13 Missing ⚠️
tutorial/image/tutorial-draw-circle.cpp	0.00%	10 Missing ⚠️
tutorial/grabber/tutorial-video-reader.cpp	0.00%	9 Missing ⚠️
tutorial/grabber/tutorial-grabber-1394-writer.cpp	0.00%	7 Missing ⚠️
modules/gui/include/visp3/gui/vpDisplayFactory.h	0.00%	6 Missing ⚠️
tutorial/grabber/tutorial-video-recorder.cpp	0.00%	6 Missing ⚠️
...ial/robot/mbot/raspberry/visp/test-serial-mbot.cpp	0.00%	6 Missing ⚠️
...utorial/grabber/tutorial-grabber-v4l2-threaded.cpp	0.00%	2 Missing ⚠️
tutorial/image/tutorial-draw-cross.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1405      +/-   ##
==========================================
- Coverage   45.85%   45.84%   -0.01%     
==========================================
  Files        1071     1072       +1     
  Lines      108360   108377      +17     
  Branches    18730    18728       -2     
==========================================
- Hits        49684    49683       -1     
- Misses      58676    58694      +18     

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