Improve integration with Agents.jl #61
Description
Right now, it is possible to use subtypes of AbstractMultilayerGraphs as graphs underlying Agents.jl's GraphSpace.
Anyway, since in Agents.jl each agent must occupy a unique position in a GraphSpace, it is not possible to have the same agent in more graph positions (which would be necessary for, say, representing a social network with multiple interaction types such as follow, like, mention, etc).