Make all references to geometric points conform to standards

[skytreader]

See: https://github.com/skytreader/PyGame-Objects/wiki/Standards-and-Conventions

Make it so that all tuples describing positions describe them as (row, col). draw_offset currently uses (width, height) and is confusing.

[skytreader]

On the other hand, check with pygame conventions and conform to that: https://www.pygame.org/docs/ref/draw.html#pygame.draw.line

Looks like pygame.draw.line expects points in the actual (x, y) format; column indices go first before row indices.

[skytreader]

More notes on PyGame conventions: font.size returns (width, height).

[skytreader]

Violation: Docstring for Drawable constructor says that draw_offset is a (width, height) tuple but GameScreen._is_drawable_clicked uses index 1 for width and index 0 for height.