Added `removed` method to document and mail builder.
Extend body class for removed documents or mails.

This allow us to display specific icons and wartermarks for removed objects.
Prefix links of removed documents with an additional removed span.

This allow us to display and additional icon in front of the regualar
icon for all removed documents in the trash listing.

An global implementation, which would work for all document_listings is not
necessary, because all removed document has to be trashed before.
Moved document and mail states to a simple class attribute.
Fixed cancel action in the remove confirmation view.
Merge pull request #691 from 4teamwork/pg_removed_styling

Prepare documents and mails for separate styling when they're removed