ConstructSampleFactors: Construct model matrix for integrating multiple samples
In kieranrcampbell/SpatialStats: Statistics for spatially resolved proteomics data

Given the output of the function BindSPE we would like to control for biases introduced by binning all the data together. ConstructSampleFactors takes the output of BindSPE and returns a model matrix of factors highlighting what sample a given cell is from

1	ConstructSampleFactors(XY, sample.ids, intercept = TRUE)

`XY`	An `X-Y-sizes` list - the output of `BindSPE`
`sample.ids`	The IDs of the samples that have been bound together - for naming the factors
`intercept`	If true an intercept is modelled when calling the function `model.matrix` but then removed from the resulting matrix so it isn't modelled twice when `lm` is later called. If false, the call to `model.matrix` is performed without an intercept, and the resulting model.matrix contains all sample factors - this matrix will have one more column that if `intercept = FALSE`.