Add the posibility to select image sizes for a tileset

Currently the images are split if their variable would be larger than 50 tokens horizontally.
A nice use case would be to allow the user to select a resolution and split that image based on that resolution.
This way, instead of a single variable, the user would get all the variables necessary to represent data in a tileset.


For example: drawing letters/numbers/symbols. It would be nice to evenly split this image in 16x16 variables.