CTRL-U (open URL) feature not working in Ubuntu 14.04 or 16.04 stock installs

## Expected Behavior
Pressing CTRL-U should open a browser window with the currently highlighted entries URL

## Current Behavior
Pressing CTRL-U has no visible effect / does not hing.
However, right clicking and using the drop-down menu option "Open URL" does work.

## Your Environment
KeePassX 2.0.2
Ubuntu 16.04 LTS, w/ current updates
QT 5.5.1
libcrypt 1.6.5


Thanks!
