[MAINT] Add and clean unit tests for ImageProcessing.

[oddkiva]

Tests are needed for:

• Deriche: cf. PR [MAINT] Fix image processing module. #123
• Determinant: WIP cf. PR [MAINT] Add unit test Determinant submodule of ImageProcessing module. #130
• Differential: cf. PR [MAINT] Add unit tests for the Differential submodule. #129
• Gaussian pyramid: cf. PR [MAINT] Add unit tests for Gaussian pyramid. #145 but better unit tests are needed.
• Extremum localization: cf PR [MAINT] Add unit tests for the localization of local extrema. #131.
• ImagePyramid: cf. PR [MAINT] Add tests for the ImagePyramid class. #133
• Interpolation: cf. PR [MAINT] Fix image processing module. #123
• Linear Filtering: WIP cf. PR [MAINT] Add unit tests for linear filtering. #124
• Local extrema: cf. PR [MAINT] Add unit tests for the localization of local extrema. #131
• Norm: cf. PR [MAINT] Add unit test for the computation of norms in the ImageProcessing module. #135
• Orientation cf. PR [MAINT] Add unit test for the computation of orientations. #136
• Scaling: cf PR [MAINT] Add unit tests for image rescaling. #144
• Second moment matrix: cf. PR [MAINT] Add unit test for the computation of second moment matrix #137
• Warp: cf PR. [MAINT] Add unit test for image warp. #146

[oddkiva]

Still need better unit tests for the Gaussian pyramid.