Add RPGcode Functions for dynamically adding/removing layer images

[swordmaster2k]

The default battle system makes use of custom functions to add/remove layer images, these should be included in the RPGcode framework.

// Adding a layer image dynamically
rpgwizard.craftyBoard.board.layers[1].images.push({src: "speech.png", x: 503, y: 267, id: "0349182b-7b6e-43ef-ac8a-ea514a7d8a6e"});

// Removing the layer image again
rpgwizard.craftyBoard.board.layers[1].images.pop();