Refactor FLEXResources.m

Previously, almost every image was an array of bytes on a single line. When most or all of the images fit into the editor, this causes the editor to page the entire (massive) file into memory.

This commit splits each massive line up into lines of 16 bytes, so that the entire file is never loaded at once. This makes opening and editing the file much faster—it used to take almost 10 seconds on a 2019 MacBook Pro.