add feature to record last clicked and last opened dates to contact record

Thanks for this extension bgm! I have been working on the same issue from a different angle - specifically, I don't want to delete the old mailings because I want to be able to track when contacts last interacted with a mailing. So, the aggregate statistics collected by this extension aren't as useful as the individual ones.

I wrote emailarchiver to capture those statistics.

Do you think these features are similar enough to justify merging the extensions?

If so, I would be happy to put together a merge request that add the code from emailarchiver to archivemailing extension.