B4 - Saving Pixel Grid #10

What?

Right now we don't have the infrastructure to start handling image exporting, and should be done later when we also implement importing images. Until then, we should allow the user to save a PixelGrid into some binary file or a text representation of the grid that can be saved and loaded from.

DOD

• User can save their grid into a file
• User can load a grid from a file and start working on it