Ligand identification in cryoEM maps with GALigandDock (#227)
This PR contains updates to density tools and GALigandDock to detect unmodeled regions of cryoEM maps and evaluate docked ligands based on their dG and density fit. Changes include:
* Adding ligand identity evaluation in multiple_ligands_ mode in GALigandDock if a density map is present
* Adding find_unassigned_density to density_tools.cc
* Adding the sim_cryo.cc app to simulate cryoEM data
* Improvements to docking large ligands, including an alternative density erosion algorithm and alternative crossover and mutations in GALigandDock