new: plot_ts_on_partition
plot merged partition for each mode
iterate over only nonzero adj elements
change from info to debug some discretize messages

don't set logging level inside transys
minor AbstractSwitched fixes
check True in label value robustly

because if label value is a string, then this causes an error.
Until now it was masked because the first disjunct (cur_val == desired_val) shadowed the second disjunct (True in cur_val).
save figs in dir from fuel tanks example
bugfix: pass None to LtiSysDyn instead of []
bugfix: correct edge orientation produced by discretize

The original discretization and merging code follows an edge orientation convention opposite to standard convention.
The result was every edge being reverted when creating a transition system from a scipy.sparse.lil_matrix using ts.transitions.add_adj, because it calls nx.from_scipy_sparse_matrix, which follows the standard convention.

Indices were also reversed in plot_partition, yielding correct plots. So the edges were reverted only in the TS and were reverted back when plotting, falsly appearing as correct, unless one compared str(TS) with the plot.

Moreover, the inconsistency was hidden in synthesis of simple examples, because liveness requires edges in both directions, reducing the likelihood of exposing this.

It was revealed by the double_tank example, because there 'normal' mode drains the tanks, whereas 'refuel' mode fills them and 'refuel' is triggered only when the tanks are low, so the problem is asymmetric. The merging code reversed the transition directions, leading to the tanks filling in 'normal' mode (!), which then never triggered 'refuel' mode and led to an acyclic result.
minimal example to test correctness of transition directions
improve plot_partition docstring
replace vprint by logging in transys