Calculate secondary structure for coarse models

[arose]

A straightforward option is the algorithm published by Zhang and Skolnick in their TM-align paper. TM-align: a protein structure alignment algorithm based on the Tm-score (2005) NAR, 33(7) 2302-2309. An implementation of it can be found in NGL (https://github.com/arose/ngl/blob/master/src/structure/structure-utils.ts).

The code should be added along the dssp implementation (https://github.com/molstar/molstar/tree/master/src/mol-model-props/computed/secondary-structure).