Add a set of JS-optimization tests: PerformanceVirtualMachineTest.

*These showcases are accompanied by two pull requests to `cocos2d-html5`: [#1015](https://github.com/cocos2d/cocos2d-html5/pull/1015) and [#1016](https://github.com/cocos2d/cocos2d-html5/pull/1016).*

I have a bunch of comments in the tests already so I'll refrain from talking too much. Feel free to ask me questions.

`VirtualMachineTestMainScene` is pretty similar to `NodeChildrenMainScene`. In fact, I think these two should be merged if I can find Ricardo.

I haven't tested these on JSB.

Test results will come later.