Simplify fitlog logic

[palday]

If we want to have fitlog contain the initial and final parameter and objective values and have the .initial, .final fields just point to those values we should expand the schema for fitlog to include the evaluation number (and increment it at the beginning of the obj function, not in the middle as is done now). Either that or abandon the idea of using thin and just incorporate a Boolean logevaluations or some name like that. I doubt very much that many users will choose values of thin other than the default, typemax(Int) or 1.

Originally posted by @dmbates in https://github.com/JuliaStats/MixedModels.jl/pull/615#issuecomment-1133067632