Created custom stylable decorator

[rob0rt]

So after some investigation, I learned that the mixin library I found doesn't really work well with React, in the sense it doesn't do field merging for static properties or function-call chaining for react built-in methods. I tried this to investigate an alternative, where I created a custom decorator for StylePropable (called Stylable) which performs the same action as using a mixin on an es5 component. So now the parallel for using StylePropable mixin in the es5 syntax is using the Stylable decorator in the es6 syntax.

This was just an experiment and I'm open to feedback. The alternative, in the style of the mixin decorator, is just making a custom mixin decorator which is React-aware. I investigated this as well, and would likely be able to use a lot of the code from the React library which does the mixin merging (I might try making a library which does this).

[rob0rt]

This is based off the second of three work arounds for mixins I discussed in #2437

[alitaheri]

Interesting work around! I like it 👍
@oliviertassinari review and merge ^^

[rob0rt]

In the future, when everything is moved, we could kill StylePropable and move all the logic into the decorator directly. This was just me not wanting to double logic.

[oliviertassinari]

Side note : this is an utility function. I think that we should move it out of the decorator at some point.

[alitaheri]

Thanks 👍 🎉