Database of catalyst surfaces for input

[rwest]

The database could contain

1. binding energies (C,H,O,N)
2. surface site densities

for each surface, like

1. Pt(111)
2. Pt(211)
3. Ni(111) etc.

These could be extracted from SUNCAT, or calculated by us from scratch (more consistent).

The choice of metal in the SMILES strings could be updated to match (see #53)