Improvement : allow colors of the grid lines to be configured in .keynavrc

[mm40]

If a user doesn't want black inner line and white outer line, he should be able to configure the colors in the .keynavrc.

For instance:
Add the following to .keynavrc to set the grid's colors:

# Colors of the grid in the following format:
# outerRed, outerGreen, outerBlue, innerRed, innerGreen, innerBlue
colors 255, 255, 255, 50, 0, 0

I've implemented this here -> 31aa431