Implement pixel grid on canvas

[jgbowser]

This issue involves splitting the canvas into a grid.
determine an appropriate size for the canvas and the number of cells.
Implement canvas painting methods that can take in a click position and determine the position in the grid that needs to be filled with the currently selected color.

[jgbowser]

with regards to the number of cells per side: 16 x 16 seems to be a standard "world square" size, whereas something like a character might be 16 x 32.

• Best options seem to be 16 x 16 or 32 x 32 to start.
• from this ^ try to determine a nice canvas size (1600 x 1600, 800 x 800, etc?)