Make WangLandauEnsemble child of TBE

Description

In connection to !367 (merged) it was discussed to make WangLandauEnsemble (WLE) a child of ThermodynamicBaseEnsemble (TBE) instead of BaseEnsemble since the WLE currently duplicates methods for swaps.

To consider

• WLE should not expose kB.
• The swap and flip moves in WLE could be inherited from TBE with some adjustments to the latter (_do_sgc_flip could be modified to accept None as chemical_potentials).
• One should check how the sublattice probabilities are handled.

Demo

• WLE child of TBE
• reduction in number of lines of code
• tests updated and pass (coverage is only allowed to increase)
• docstrings must be understandable also from WLE perspective