All forcefields are parsed on run

[pckroon]

When running Martinize 2 it parses all forcefields, instead of just the ones needed. This means that if a FF you don't need and is not yours contains a sytnax error the entire program stops. It would be more elegant to only parse those forcefields required. This would also help in coverage measurements, since currently when vermouth is imported it also imports all forcefields, generating false coverage data for those parsers.