Mismatch of tile after reload, changing row or col number, or after first install of the app.

When clicking several times and quickly on the reload button, the bug often occurs: the free tile is not at the right place.

I suspect this is due to bindings, currFreeTile may be not updated in the order I expect.

To solve this, I cause a complete re-initialization of the mainPage by:

• create a signal newGame()
• on this signal: clear the page stack (to destroy current page), create the new game, and push the mainPage (which will restart with new game settings.
• trigger this signal when a new game is requested (reload button, or from settingsPage)