Implement CanonicalEnsemble

Description

As a first example for a functional ensemble derived from BaseEnsemble (#162 (closed)) the canonical ensemble shall be implemented. This includes

• a trial move
• an acceptance/rejection condition
• ensemble specific kwargs and properties (temperature)

Notes

• in this first version the energy change is to be computed using a total energy calculation (see #167 (closed))
• a smart strategy for computing the energy change due to different types of moves (also relevant for other ensemble will be discussed elsewhere)

Sub-tasks

• trial move
• acceptance/rejection
• kwargs, properties
• unit test
• add basic example

Demonstration

• all tests pass
• complete docstrings
• example available