Add MCMC options in the settings

[IvanHeriver]

MCMC settings to add are:

• adaptation iteration count
• cycles count
• burn factor (proportion of MCMC samples to discard)
• slimming step (step for removing MCMC samples)
• minimal move rate
• maximal move rate
• down multiplicative factor
• up multiplicative factor

Feel free to add/remove other options.

Also, if other ideas for settings that are not related to MCMC, feel free to add them as well.