fix for issue #379

Fixed normalization issue in phonon data, added new derived metainfo for specific vibrational free energy, added ability to fetch thermal data from the API.

Refactored the band gap information to support more spin channels and easier querying for band structures without band gap.

Removed section_k_band normalized, as it can be simply constructucted from section_k_band with a shift stored in energy_reference_highest_occupied. Made section_encyclopedia to store references into the band structure instead of constructing own copy.