Port to Drupal 7

This should really be an easy task.
The only thing that needs to tackled I think, apart from various code style / formatting changes is the hook_block implementation. And of course dependent on a 7.x version of Date API, but we're only using date_format_date, which is a pretty low-level function, and probably doesn't even need to be ported.

Not working on this for now, just wanted to open up this issue to remind myself to do this at some point.