Fixes mesa#1821.

This provides a declarative interface to plotting multiple lines in 1
chart.

Example usage for virus on network
```python
page = JupyterViz(
    VirusOnNetwork,
    model_params,
    measures=[
        # This is subject to change, as it could have been
        # {"Infected": {"color": "tab:red"}}, but let's keep it simple.
        {"Infected": "tab:red", "Susceptible": "tab:green", "Resistant": "tab:gray"},
        # Alternatively, if you don't want to manually specify colors:
        # ["Infected", "Susceptible", "Resistant"],
        make_text(get_resistant_susceptible_ratio),
    ],
    name="Virus Model",
    agent_portrayal=agent_portrayal,
```