Modifications for the upcoming Render-Based Tracking submodule

[SamFlt]

This PR introduces small modifications and improvements that were required for the Render-Based Tracking submodule that is coming soon (hopefully :-)). It contains:

• Changes to vpMeSite:
  • Introduction of a new method, trackMultipleHypotheses, that retains the K best candidates instead of only one.
  • Small modifications to the track code to cleanup code redundancy, removed the use of an array that was not needed.
• Some improvements to the rendering pipeline
  • Some optimizations in the normal pipeline (although pretty insignificant).
  • Cleaned some code and refactored some variables
  • Added the auxiliary methods to render, that are called before and after rendering. This allows for inheriting classes to further process data before rendering.
  • Improvements to the tutorial code and documentation.
  • Cleared transform on loaded models: this led to inconsistencies, as BAM files saved the Object-to-world transform.
  • Better clipping value computation.
• Introduction of a new functionality in vpDisplayFactory: makeDisplayGrid that creates a display grid, initializing the displays with the given images. This supports variable grid size, with padding between displays.
• Modified the vpImage copy operator: The previous version always resulted in new/delete operations: this is not necessary when image dimensions are the same.
• Introduced the vpImage move assignment operator which was missing: the default one led to a memory leak.

[codecov]

Codecov Report

Attention: Patch coverage is 55.76923% with 69 lines in your changes missing coverage. Please review.

Project coverage is 45.42%. Comparing base (84d0d80) to head (983d558).
Report is 39 commits behind head on master.

Files with missing lines	Patch %	Lines
modules/tracker/me/src/moving-edges/vpMeSite.cpp	18.33%	49 Missing ⚠️
modules/io/src/tools/vpJsonArgumentParser.cpp	78.04%	9 Missing ⚠️
modules/gui/include/visp3/gui/vpDisplayFactory.h	0.00%	4 Missing ⚠️
...odules/core/include/visp3/core/vpImage_operators.h	87.50%	3 Missing ⚠️
modules/tracker/me/include/visp3/me/vpMeSite.h	60.00%	2 Missing ⚠️
modules/tracker/klt/src/vpKltOpencv.cpp	0.00%	1 Missing ⚠️
modules/tracker/mbt/src/vpMbGenericTracker.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1456      +/-   ##
==========================================
+ Coverage   45.41%   45.42%   +0.01%     
==========================================
  Files        1110     1110              
  Lines      110531   110643     +112     
  Branches    18925    18944      +19     
==========================================
+ Hits        50199    50264      +65     
- Misses      60332    60379      +47     

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[fspindle]

@SamFlt Thanks