Add testing to the example

[avh4]

This is a first stab at adding testing to the starter project using deadfoxygrandpa/Elm-Test.

Tests can be run with ./run-tests.sh, but requires that npm is available and is able to install jsdom@3.

Possible improvements:

• have a web-based runner for people who can't use IO

[evancz]

This really makes me want to sort out the testing stuff! I want to keep this open as a super simple use case to design for when making elm-test work properly. Is that a crazy thing to do?

[avh4]

Yeah, that sounds like a great plan to leave the branch as an example for adding testing support.