refactor HybridSysDyn and test it

env_labels, disc_sys_labels become explicit arguments to HybridSysDyn.__init__.

env_labels, disc_sys_labels are now properties, so protected from changing.

If no env_labels or disc_sys_labels are provided, then they default to ints, with warning. The ints are not saved, but instead returned using range upon access.

If the number of mode labels does not match disc_domain_size, or len() is undefined for them, then again the default ints are used.

The previous version defined labels as given, even if they didn't match the dynamics keys, in which case ints were compared to dynamics keys.

- logging messages
- docstr restructured
allow for missing mode combinations in HybridSysDyn
warn if missing env,sys mode combinations in HybridSysDyn
check each HybridSysDyn mode has PwaSysDyn dynamics
new: HybridSysDyn.__repr__
new: PwaSysDyn.__repr__