nerd again

Because work is boring and I needed to do it anyway, here's a new version of evo-mail-notify.

Changes:

- Refactored the bundle of code from the previous version into a proper class
- Added tooltip support (if you hover over the indicator, it'll tell you which subscribed folder the new mail is in)

I'd love to add a field to the tooltip that tells you how many new messages there are, but evolution doesn't put that information in its D-Bus signal...