webadmin: fix truncated lined in "New Template" dialog

Make the editor width 100%

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=951055
Change-Id: Idea8be2ad3d9e1c812edb9e5c4d126413e67b2a5
Signed-off-by: Roy Golan <rgolan@redhat.com>