Tails Installer requires a GTK version newer than the one in Ubuntu 14.04 LTS

When I execute `liveusb-creator-launcher` in Ubuntu 14.04 LTS (Trusty) I get an error about needed GTK 3.14 while GTK 3.10 is installed. In Ubuntu 14.04 LTS (Trusty) they have GNOME 3.10 (which in Debian stable we have GNOME 3.14). GNOME 3.14 appears in the latest release (Ubuntu Vivid 15.04).

Our package should be installable on Ubuntu 14.04 LTS (Trusty).

Feature Branch: 451f:liveusb-creator/feature/jessie

Parent Task: #8549 (closed)

Original created by @sajolida on 10406 (Redmine)

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