Fix NDPluginStats dimension assignment

[OCopping]

This PR aims to fix NDPluginStats and allow for using the "Profiles" tool for colour cameras. Currently the code manually assigns Dim 0 and Dim 1 to sizeX and sizeY respectively, but this is only the case for mono cameras. For RGB cameras, Dim 0 is used for RGB channels.

Instead I propose we use a the same logic as use in NDPluginROI, where getInfo determines the correct variables, based on the number of dims and the selected colour mode, and assigns it to an NDArrayInfo_t structure that is returned to the script for better assignment.

Fixes #541

[MarkRivers]

I don't think this is going to help with your goal of producing profiles for color cameras. NDArrays for RGB color cameras have 3 dimensions, [NX, NY, 3]. Note that the documentation here:
https://areadetector.github.io/areaDetector/ADCore/NDPluginStats.html
says this:

Each calculation can be independently enabled and disabled. Calculations 1 and 4 can be performed on arrays of any dimension. Calculations 2 and 3 are restricted to 2-D arrays.

Calculations 2 and 3 are centroids and profiles. This is enforced here:

ADCore/ADApp/pluginSrc/NDPluginStats.cpp

Line 205 in 56eecf2

if (pArray->ndims > 2) return(asynError);

and here:

ADCore/ADApp/pluginSrc/NDPluginStats.cpp

Line 338 in 56eecf2

if (pArray->ndims > 2) return(asynError);

[OCopping]

Closed re- conversation in #541