Adding axis indicating dimensions of game screen

[kmsalah]

Specifying the position of objects on the screen can be confusing if you don't understand the direction of the axes and the dimensions of the screen. Adding basic xy grid lines to the left and bottom of the game screen in the editor could clear the confusion.

[kmsalah]

To start off:

• in the html/index.html file place a checkbox anywhere on the front page.
• in the scripts/editframe.js, create a new function like at line 199 #QR or line 205 #Update