Prepare support for non-square grid sizes

[deepnight]

Save separate width/height for grid infos in JSON, for future non-square grid feature (#18, #291)

• [ ] update LayerDef.gridSize / scaledGridSize
• [ ] update Project.defaultGridSize
• [ ] update Tiled exporter
• [ ] update Ogmo importer

[daimahou]

I'm planning to add this feature, I haven't got too deep in reading the code yet, but do you have some pointers, important things to consider, ect... to implement this ? Would be cool if there was some kind of documentation on the architecture of the app for example. Thank you.

[daimahou]

Im halfway done implementing it.

Still got a few bugs to iron out, but I can help you integrate it back into the main app if you'd like. I had to make some modifications to the ldtk-haxe-lib to get it work. I also need to modify deepnightlibs/ 's pixelGrid.

(I didnt touch ogmo or tiled importers though as I dont need the feature myself, I simply disabled them)