Username as notification title

[enh] Notifications of column update display the username the column belong to as title. It doesn't display the title of the column but I don't think it's a very relevant info.
It adds a string to translate; I don' t know how to handle this.

Fixes issue #234

Preview (in Gnome-Shell) :
![notif_turpial](https://f.cloud.github.com/assets/1036656/2368489/af02b6f4-a7ac-11e3-9895-6516f8db58d3.png)