Clear All button in the Menu

[SushantGautam]

I think it's worth having a clear all button in the Menu.
We can fire an alert for confirmation to prevent accidents.
This can be disabled by default but if there is such an option in config. to enable the button it can be very handy for teachers who resue the board.

[lovasoa]

Duplicate of #92

See

• Erase all button on menu #152
• Add one click clear button #202