Version 0.4.5 - faster rendering and proper randomization

It's been a minor change in functionality, but major rewrite. The Overlay presets rendering is completely new now. In future it will be the only type of rendering, Corner-type will be removed, as Overlay can in its current state accomplish everything Corner one can. I plan for 0.5 a major UI rewrite, so that's when it is scheduled.

Changes:

- faster render for Overlay presets, it was an issue with 255-tile template

- proper randomization for those presets: before random tile variants number was based on the amount of part variants, now on the amount of the same tile in the template

- tile parts of one type in a tile now have the same random seed (the source for the picture is overlay_8_pixelart_random.png in examples):

- Mac export is excluded for now (see previous devlog)