Add intensity profile along a segment

[PierreRaybaut]

Regarding intensity profile extraction on images, DataLab currently implements the following:

• Intensity profile extraction along an horizontal or vertical line
• Intensity profile extraction averaged horizontally or vertically withing a rectangular area
• Intensity profile extraction averaged radially, around a center (centroid, image center, or custom coordinates)

The purpose of this Issue is to implement the intensity profile extraction along a user-defined segment (both graphically and by entering points coordinates).

[PierreRaybaut]

This will require to upgrade PlotPy dependency to V2.1.