Fix warning message shown in browser console to avoid using depreciated class from react version >=15.5.0

[lynnchin]

• Added prop-types and create-react class package module via npm;
• Fix existing code to use prop-types and create-react-class library instead

[chenglou]

Hey! Thanks for the PR, but I've already merged #47. That'll teach me to review PRs in reverse order... Sorry about that.

Tbh I kinda prefer this change since it's fewer things changed. But since the community is moving toward es6 classes I guess I'll keep up the pace.

Thanks a lot =)