Unique canvas ID and fixes

I'm adding in a unique id for each canvas created. This makes it possible for scripts to do cool things in the future as well as helps things like the Atlas Maker to be able to better save state in projects.

Features

• Added internal unique id to each canvas
• Atlas Maker now saves your clips to the project

Fixes

• Fixed an issue with the needed size calculation of atlases (causing failed exports)
• Fixed an issue with weird scrolling behavior in the Atlas Maker