Remove winmail.dat preference removes additional attachments

[dugite-code]

The Remove Winmail.dat preference in the webextension re-architecture causes additional attachments such as forwarded emails to be removed as well.

It is questionable if this is the wrong behavior or not as Microsoft emails do not send additional attachments or not. It may be advisable to keep additional attachments in a future version update.

[jobisoft]

Could you release v6.1 with this fix?

[dugite-code]

Yep, I was hoping to be able to get #35 done along side but had some other thing come up.

Uploaded awaiting review