Add icon export functionality to mymc++ command line interface

[Issung]

MYMC originally came with a cli interface, it works well and maybe some users will want to use it for automation, add the new icon export functionality to that interface.

[Issung]

Probably want a option on the cli to specifiy the output folder to be anywhere.
Probably requires a bit of a refactor to loading the icons, at the moment the exporter gets the icon asset data from the renderer window.. lol.