Add mcse plots similar to neff and rhat plots

[jgabry]

This PR is not new, just a reworked version of PR #210 from @VeenDuco. For some reason that PR got messed up and it lists 223 files changed when there should only be a few. This separate PR includes what I think were the intended changes from @VeenDuco, which I had already looked at and approved (so I think this is ready to go). I also added a few tests.

@VeenDuco would you mind taking a quick look at this before I merge it?

[VeenDuco]

Hey @jgabry, I think most looks good. Only in R/mcmc-diagnostics.R there are still some occurrences of labels = c("low", "ok", "high") instead of labels = c("low", "mid", "high"). I think everywhere else ok was replaced with mid. Everything else is a quite straightforward adaptation of the other functions and looks good.

[jgabry]

Thanks @VeenDuco.

Only in R/mcmc-diagnostics.R there are still some occurrences of labels = c("low", "ok", "high") instead of labels = c("low", "mid", "high").

Can you point me to where you still see "ok" in the code? I can't seem to find it. Thanks! (I agree it's fine to keep "ok" in the doc)

[VeenDuco]

My bad, those were still there in the commit ccdac30 but corrected in adecf0b.