if no transitions given to plot_partition, then plot adjacency

- this makes PropPreservingPartition.adj easily vieweable, w/o the need to explicitly pass it as previously: plot_partition(ppp, trans=ppp.adj)
- to avoid confusion, clarify in plot title where the transitions came from
- if no adjacency given to PropPreservingPartition.__init__, initialize it to None
restyle indents of AbstractSysDyn docstring
new: Polytope.__eq__, Region.__eq__
guard polytope.is_subset from an arg which neither Polytope nor Region

this surfaced by a Polytope comparison to None using == instead of "is"
create dicts of original_regions, ppp2orig for switched systems