Button to toggle between add/remove mark and set answer

[plhosk]

First of all thank you for the game. The great app named HoloKenMod, which no longer works on the latest Android, has a toggle button that makes it very fast to switch between two input modes:

• add/remove mark
• set answer

When in set answer mode, the next press of a number sets the cell to that number, equivaent to the long press in Gauguin.

While an answered cell is highlighted, togging the mode to add/remove mark changes the answer back into a mark.

This would help by eliminating the need to wait 1 second for each answered cell. In a 6x6 game this is 36 seconds of waiting for the UI. It would be great to have this as an aternative to the long press.