Allow fully flagged Cells to be pressed

## Description
When a fully flagged Cell is pressed it should open all Cells connected to each other that are not Bombs.
If the ones being revealed immediately nearby are Bombs then that means that a flag was incorrectly placed and the user should lose the game.
[See here for the functionality in action](https://minesweeper.online/game/926223191).

## Difficulties
- How would this different behaviour work with the existing logic of revealing / checking Cells?
Existing logic might need to be changed to accommodate this behaviour.