NF: Enable grid.
NF: Grid may be activated using a button.
Merge pull request #261 from Debilski/feature/draw_grid

NF: Enable grid.
BLD: Activate Python 3.4
Merge pull request #263 from Debilski/feature/python-3.4

BLD: Activate Python 3.4
BF: Need to reset the bot_error status before each step.