Better user output

[pckroon]

Martinize2 (and vermouth) currently are very quiet about what they do, especially around input and DSSP. It would be valuable for the users if they became more verbose, and told e.g. how many molecules/residues/atoms were read, how often dssp was run, what the output was, etc.

@Tsjerk can I assign this to you? You did a great job on this for martinize1, so maybe you can do it again :)