styling for title field; correct input target in tests; make download filename safer with default, max length; in playground index, correctly pass props through to gui container

on what to do when linking or so didn't work correctly

- Add documentation on how to run tests.

Full exposition here: https://github.com/LLK/scratch-gui/wiki/Publishing-to-GitHub-Pages

* Remove unnecessary dev dependencies

* Use large range on true "dev" dependencies

The exact versions of these dependencies are not important for building, so give them large ranges in order to quiet down greenkeeper.

I did not split them between dependencies and devDependencies because a package's dependencies are installed whenever the package is installed as a dependency. Installing all of these would be obnoxious and unnecessary.

Also remove outdated notice about PRs

https://greenkeeper.io/