[UIFe] Updated icons for the messaging menu

[Sebastien Bacher]

Hey everyone,

The Canonical designer would like to slightly tweak the 
indicator-messages icon to fix some of the background-contrast-issues 
with the current set.
Those don't change the form or color of the icons and should invalidate 
the documentation screenshots...

The bug used for the UIFe is
https://bugs.launchpad.net/ubuntu/+source/ubuntu-mono/+bug/1056488

You can get the update package for testing in 
https://launchpad.net/~ubuntu-desktop/+archive/ppa (ubuntu-mono 
uploaded, humanity-icon-theme to follow)

Thanks for considering the update,
Sebastien Bacher