Reworked PasteItem tests (use ftw.testbrowser instead of OGBrowser).

(cherry picked from commit fdde491ce20398791caffc9a214afa39276058e7)
Adjust available expression for paste action.

Use `object` instead of `folder` to call the `is_pasting_allowed`, because it's
not guaranteed that all folder allways returns the current context.

(cherry picked from commit f1844eb35f897b27141cd415d62149b7c2f862ca)
Disable paste action for mails.

(cherry picked from commit fdd6071f82c6a396fa854bb953c53b83a709d7d0)
Reworked extract attachment tests.

(cherry picked from commit e99158b7afaf880f7899a586888f7525cc4d478f)
Extract attachments view: fixed icon display in attachment listing.

(cherry picked from commit 75c29373993ffdf4afbf7158ab1995f23c73134b)
Merge pull request #670 from 4teamwork/pg_4.0.4

Backports for the 4.0.4 release