Add notice to CMA-ES to explain it does not support 1d problems

[MichaelClerx]

I can describe the phenomenon, as it appears in my own work: I am working with an SEIR model for which I am trying to infer one parameter beta. I use my usual approach in which I write up a pints.LogPDF, pints.LogPrior and a pints.LogPosterior objects, and then when I try to run it (with 3 chains, so is not that issue), I get this error message:

Originally posted by @I-Bouros in #1520 (comment)

We should add a notice to the pints.CMAES wrapper to say 1d is not supported, and raise a more informative exception from its constructor (to clarify that PINTS supports 1d in general, but this particular method does not, and please choose another method)