UIFe: Unity Mail desktop actions should not be shown in the Messaging Menu

[Dmitry Shachnev]

https://bugs.launchpad.net/ubuntu/+source/unity-mail/+bug/1055972

Unity Mail currently displays four static actions from the desktop
file in the messaging menu: "Home", "Inbox", "Compose mail" and
"Change accounts details". These actions are useless there (because
they duplicate the launcher quicklist) and waste space. This is caused
by a behavior change in indicator-messages (see Lars' comment in the
linked bug). I want to remove two of those actions from the menu by
adding a NotShowIn header.

This is a universe package and not documented in the official Ubuntu
documentation.

No translations change is needed, but subscribing ubuntu-translators anyway.

Cheers,

--
Dmitry Shachnev