Normalising avatar textures programatically

[calummackervoy]

In Avatar.gd there is a function init_new_player, which initialises a new player with (amongst other things) their portrait

Currently all portraits are 512*512 in PNG format and the code takes advantage of that

In order to accept portraits from the internet we should accept different sizes (although it's OK to put some restrictions like filetype on the portrait). So the code here needs to be adapted based on the image size

Ideally we would also place a circular filter on the image so that they're always round although this might be easier in JavaScript

[calummackervoy]

This need is repeated for the sprite in objects/cards/Card.gd