One-convo models with convos=[]

[snotskie]

When conversations is an empty array [], the model should behind exactly as though we manually did [:All] instead, to have a model with a single large conversation

This may actually be the case as-is, but it needs to be confirmed and tweaked if needed

[snotskie]

staged in https://github.com/snotskie/EpistemicNetworkAnalysis.jl/commit/8011e48cb8b716ba9c2de0267e80dec29d9b2f5b

turns out, it was actually already possible, but I had to fix this infinite recursion problem:

# Wrapper constructor, accepts any type for codes etc.
function constructENA(
        ::Type{M},
        data::DataFrame,
        codes::Array{<:Any,1},
        conversations::Array{<:Any,1},
        units::Array{<:Any,1},
        rotation::AbstractENARotation;
        kwargs...
    ) where {R<:AbstractENARotation, M<:AbstractENAModel{R}}
    return constructENA(
        M,
        data,
        Symbol.(codes),
        Symbol.(conversations),
        Symbol.(units),
        rotation;
        kwargs...
    )
end

become

# Wrapper constructor, accepts any type for codes etc.
function constructENA(
        ::Type{M},
        data::DataFrame,
        codes::Array{<:Any,1},
        conversations::Array{<:Any,1},
        units::Array{<:Any,1},
        rotation::AbstractENARotation;
        kwargs...
    ) where {R<:AbstractENARotation, M<:AbstractENAModel{R}}
    return constructENA(
        M,
        data,
        convert(Array{Symbol}, Symbol.(codes)),
        convert(Array{Symbol}, Symbol.(conversations)),
        convert(Array{Symbol}, Symbol.(units)),
        rotation;
        kwargs...
    )
end

This is the method that converts whatever type you give the config arrays to Symbols. However, Symbol.([]) has type Array{Any}, so this method recurses infinitely. Also adding an explicit convert fixed the problem, and the resulting behavior for conversations=[] was exactly what we wanted