Configuration and Structure conversions

[bpuchala]

• Adds Configuration.to_structure and Configuration.from_structure
• Adds ConfigurationWithProperties.to_structure and ConfigurationWithProperties.from_structure
• Add Python tests for Configuration and Structure conversions
• Bug fixes in config::FromIsotropicAtomicStructure
• Enable config::FromIsotropicAtomicStructure to read Structure strain from all strain metrics (previously only Ustrain was read)
• Create config::ToAtomicStructure class for basic Configuration to SimpleStructure conversions
• Prevent conversions from float to int for integer arrays in libcasm.configuration

[bpuchala]

Note that this should pass tests if the current 2.X branches of CASMcode_crystallography and CASMcode_mapping are installed.