Test more behavior in conversion

[josephmckinsey]

• We want to test time-series λ, μ
• Test a HybridSystems:
  There is a known past bug here in duplicating between generatorstorages and storages
• Unit test line_and_interfaces.jl
• Unit test util/sienna/helper_functions.jl
• Better test the network representation
  Ideally we would test whether the power-flow from MinCostFlows.jl respects Sienna constraints and whether the flows are roughly similar in some way.