Add canvas size to exported FULL json file.

[Pavlo Holotiuk]

Problem
No canvas size in exported files. I'm writing a tool which converts exported files into a map mod for a game. The only file currently having this informaition is the .map file. And not in json part of it. It requires custom parsing which shouldn't really be a thing.

Solution
Add canvas size to full json file. Probably to "settings" object.

Alternatives
Add Burg lon, lat coordinates to json or a separate Burg geojson export option.

[Azgaar]

Added width and height to the info object. Did not add to settings as settings are supposed to contain elements that can be changed. Map size cannot be changed.