[WIP] New photometric VS features + improvements to vpFeatureLuminance

[SamFlt]

This PR introduces new visual servoing features, taken from the papers of Eric Marchand and readapted from his code.

These features are PCA and DCT compressed representations of the luminance information.

In terms of implementation, new classes are introduced:

• vpFeatureLuminanceMapping a visual servoing feature, which combines a vpFeatureLuminance object with a vpLuminanceMapping subobject. This is the feature that is given to vpServo
• vpLuminanceMapping, a common interface for mappings that operate on luminance information. a map method computes a vector representation from the image. The inverse method, converts this vector back to an image, with some information loss. Finally, the interaction method computes the Jacobian, given the image, the compressed representation and the photometric Jacobian (computed beforehand by vpFeatureLuminance when used with the vpFeatureLuminanceMapping)
• The vpLuminanceMapping interface has two implementations: vpLuminancePCA and vpLuminanceDCT. they can be used interchangeably in vpFeatureLuminanceMapping

Before this PR is complete, several things are lacking:

• Encapsulate a Levenberg-Marquardt control law in a custom class.
• Add weighting mask when computing the error in vpFeatureLuminance
• Add an option to have a depth per pixel instead of considering that all 3D points are at an equal distance from the camera.

[SamFlt]

@fspindle,

If the CI is ok, this PR can be merged. I will write a followup PR to implement the remaining features when I have some time :)

[codecov]

Codecov Report

Attention: Patch coverage is 83.13609% with 114 lines in your changes missing coverage. Please review.

Project coverage is 45.86%. Comparing base (f95b137) to head (6564493).
Report is 108 commits behind head on master.

❗ Current head 6564493 differs from pull request most recent head e9e69f1

Please upload reports for the commit e9e69f1 to get more accurate results.

Files	Patch %	Lines
...s/src/visual-feature/vpFeatureLuminanceMapping.cpp	75.53%	68 Missing ⚠️
...sual-servoing/photometricMappingVisualServoing.cpp	80.00%	36 Missing ⚠️
.../visp3/visual_features/vpFeatureLuminanceMapping.h	62.50%	6 Missing ⚠️
...features/src/visual-feature/vpFeatureLuminance.cpp	77.77%	2 Missing ⚠️
...ual_features/test/feature/testLuminanceMapping.cpp	98.96%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1359      +/-   ##
==========================================
+ Coverage   45.55%   45.86%   +0.30%     
==========================================
  Files        1082     1086       +4     
  Lines      109238   109887     +649     
  Branches    18658    18876     +218     
==========================================
+ Hits        49767    50396     +629     
- Misses      59471    59491      +20     

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