Read/write loses info in _ma_template_non_poly.details

[gtauriello]

Related to example files in #42 (SM_model_01.cif processed with read_write.py or make_mmcif.py).

Observation: _ma_template_non_poly.details gets reset to "." instead of keeping the value which is otherwise set according to entity description. The entity description is kept and set properly but somehow this gets lost in _ma_template_non_poly.details.

Expectation: _ma_template_non_poly.details keeps the value as in the input file.

[benmwebb]

Clarification: while this table uses the entity description, it's the template entity, not the target entity, and template entities aren't stored in the mmCIF (they are only referenced by ID).