Introduce expert mode and show 'Analyze' button in that mode

The button is visible only in expert mode but keyboard shortcut is
enabled all the time. (Ctrl+Alt+Return)

Closes abrt/abrt#634

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Signed-off-by: Richard Marko <rmarko@fedoraproject.org>