Changed price_changes to JSON reducing the amount of work on XML and make it work

The format to send price_changes in JSON is the following:

price_changes = [
	{'color': {'blue': 99, /*'color': price, */}},
	{'size': {'XGG': 1000, 'GG': 500, 'G': 100, '42': 9}},
	// {'another-attribute-code': {'some-value': some_price}}
]

Also, I fixed some crashes on PHP where using classes as arrays, by casting it into array.