webadmin: unescape cell tooltips string values

SafeHtmlCellWithTooltip -> getTooltip:
Unescaping title's text value to prevent tooltips
with escaped characters/html tags (unrendered)
[it should be safe since browsers natively render
title attributes as string].

Example screenshots:
* escaped (current) - http://imgur.com/8aNIouV
  unescaped - http://imgur.com/nQFP0jx
* escaped (current) - http://imgur.com/9HxHA4H
  unescaped - http://imgur.com/8wzOUVE

Change-Id: I2da6812694737c212352afda48fa9a50e97f8d60
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1001851
Signed-off-by: Daniel Erez <derez@redhat.com>