bugfix: check AP labels from regions of mode partitions
pass correct number of args to merge_abstractions
annotate TS with AP labels of regions of merged partition
bugfix: str_modes intended to be a dict
return abstraction from discretize hybrid
new: AbstractSysDyn.plot
rename discretize_hybrid to discretize_switched

because switching is a special form of hybridness.
discretize_hybrid doesn't distinguish from discretize, because PWA systems are a special form of hybrid systems.
test for discretization of switched systems