Visualization not compatible with POMDPs.jl ecosystem

[dylan-asmar]

Current visualization components aren't compatible with the rest of the POMDPs.jl ecosystem. In particular, this problem currently doesn't work with DisplaySimulator or GifSimulator without some modifications.

Warning: No implementation of POMDPTools.render(m::VDPTagPOMDP{Nothing}
│   mdp: VDPTagMDP{Nothing}
│   meas_cost: Float64 5.0
│   active_meas_std: Float64 0.1
│   meas_std: Float64 5.0
│ , step) found. Falling back to text default.
└ @ POMDPTools.ModelTools ~/.julia/packages/POMDPTools/7Rekv/src/ModelTools/visualization.jl:31
ERROR: MethodError: no method matching show(::IOStream, ::MIME{Symbol("image/png")}, ::String)