Add option to use the Mocha test framework

[necolas]

Now that there are extensions to Mocha for Flight - https://github.com/naoina/flight-mocha - it should be an option in the generator. Perhaps even the default.

[necolas]

Would need to install an assertion and spy library too. I've used Chai and Sinon…but IE8 support would be good, so might have to look around for alternatives.