Resolve "Clean up handling of parameters and attributes in ensembles"

Summary of changes

This is a list of changes done in this branch:

• Parameters in docstring sorted in the order they are called in the arguments.
• accepted_trials, boltzmann_constant and total_trials have been made private.
• data_container_write_period is a property with a setter in base ensemble.
• Ensemble parameters(temperature, ...) are read-only properties in all ensembles.
• atoms and calculator are positional arguments without default
• PEP3012 was removed and missing keyword exceptions re-implemented
• Attribute section cleared out

Unittest and tutorials (only code part) updated accordingly.

Closes #264 (closed)