Show a status bar in the window

The user interface should show the status of the game. Add a status bar
to the window where this will be displayed. The status bar is added in
code since that's how the grid is added to the window, but it is
probably a good idea to move this to the UI file some day.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Set status bar to Game Over upon finding a flower

The text on the status bar should be updated when the user finds a
flower with the text Game Over. Make the grid emit a signal when this
happens and update the status bar accordingly.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>