Export entire receptor with updated positions of flexible sidechains

[diogomart]

Currently, the positions of flexible sidechains simulated during docking can be retrieved for each sidechain in isolation. The user then has to manually copy-paste the updated positions into the original receptor structure to get a model of the entire receptor with updated sidechain positions. This should be handled by the receptor data structure (chorizo). @nbruciaferri already did work toward this goal in 8a9b5ec
The need for this feature has been mentioned in ccsb-scripps/AutoDock-Vina#319