add pre-processing plot functionality

[connor-french]

Description

Provide plotting functionality to view raster/array outputs easily and facilitate model checking

Ideas:
Split plotting functions into multiple functions:

• plot_landscape #22 - plot the demes as a static map to check the transformation quickly
• plot_model #23 - plot the demes and migration rates for a given timestep as an interactive map
• plot_timeseries #24- plot the total landscape size change over time or the deme size change over time for a particular deme

I think demo_table (#25) can be something that gets added later, but the other three functions should be implemented first.