Various Improvements

Building on yesterday's optimsations, here are some changes to make the system more usable.

Switching to Mailcore2 means that 'send directly' is now working again (at least for me).

Notes: MailCore2 [might not be 10.7 compatible](https://github.com/MailCore/mailcore2/issues/566#issuecomment-34891672) so if this is OK we should probably make the plugin 10.8+ only