applet: remove confusing "Show" button

- the button was opening problem's web page
- since applet opens the gui with preseleceted problem and the gui
  provides clickable links to problem's pages, Show button is no
  more necessary

- related to rhbz#905412

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>