New constructor for EnsembleParameterTable

[Maximilian-Stefan-Ernst]

          Maybe we want to have something like this:

EnsembleParameterTable(ps::Pair{K, V}...; params = nothing) where {K, V} = EnsembleParameterTable(Dict(ps...); params = params)

So users can just write

partable = EnsembleParameterTable(:Pasteur => specification_g1, :Grant_White => specification_g2))

instead of having to construct the Dict themselves every time:

partable = EnsembleParameterTable(
    Dict(:Pasteur => specification_g1, :Grant_White => specification_g2),
)

Originally posted by @Maximilian-Stefan-Ernst in #203 (comment)