Updating Contributing documentation:
* Adding reference to spec repository for feature development
* Adding localization issue template
* Adding clarifications for contributions and PRs
Saved 301 KB out of 9.2 MB. 15.8% per file on average (up to 82.2%)
Fixes #.
Saves 301 KB (although not all files are included in the build)
Description of the changes:
For PNG files: used a combination of Pngcrush, OxiPNG, AdvPNG, PNGOUT and Zopfli
For GIF files: used Gifsicle
How changes were validated:
No changes to behaviour or source code.
Previewed the changed files to make sure they still work