reshape_samples: Reshape fitted scores for easy plotting
In krisrs1128/nmfSim: Helpers for Conducting Simulations with NMF

Both thetas and betas in NMF are reshaped using very similar code, so we might as well combine it explicitly in one function.

1	reshape_samples(samples, truth, dims)

`samples`	[array] The samples generated by STAN; e.g. obtained by fit$param. Two dimensions are for the actual matrix, the third are from sampling iterations.
`truth`	[matrix] The truth parameter values, known because we are working from a simulation.
`dims`	[character vector] The names to use for the rows and columns of the parameter matrix.