Feature/pngcrush

This changes over 3000 files, but there should be no content change.

Ran the following:
```bash
find . -name '*.png' -exec pngcrush -reduce -fix -new -ow {} \;
```
I did *not* pngcrush any files shipped from third parties, so nothing under `ui/node_modules` or `ui/client/third_party` has been crushed.

Results:
```
$ git checkout develop && du -sch . | grep total
679M	total

$ git checkout feature/pngcrush && du -sch . | grep total
652M	total
```