Send game-progress signal when something happens

The grid view should send a signal when some action happens. Call it
progress and emit it in the tile state set callback.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Expose number of flowers and marks

There should be a way for a caller to get the number of marks and
flowers from the grid view. Add the appropriate getter functions to it.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Show current number of set flags in status row

Let the window listen for game-progress signals. When emitted update the
status text to say the number of flags currently set.

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