WIP: Add FlatList implementation

[jaischeema]

This is still very much in works but I wanted to get some feedback if is the right approach. We are currently encoding/decoding the data on every render data, not sure how efficient that would be.

Next step would be to implement shouldItemUpdate method to make it more efficient.

[jaischeema]

@jsteiner Hi Josh, I saw that you implemented ListView and talked about using FlatList in your commit message. Can you please take a look at this and give us some feedback?

[ohanhi]

@jsteiner, do you have any comments for this?

[jsteiner]

Sorry for the hold up. Got lost in my inbox. I think this is a good first pass.

[jaischeema]

Thank you for the feedback, I'll clean it up and get rid of the WIP tag as well. React 0.43 has been released, will make sure nothing else breaks with that.

[ohanhi]

@jaischeema Thanks for you work! Are the changes to the Counter example intentional?

I think we should consider moving the examples in their own repository/repositories, especially since everyone who uses elm-native-ui will also download and self-publish all the examples to their elm-stuff.

[jaischeema]

@ohanhi No, they are not intentional, I will revert those. I think its time to add the UIExplorer project to showcase different components and keep only one one Counter example in the repo to help with the initial style. I will create a new project and add all these examples as a part of that and remove the ListDemo from this PR. If you can create another repo to host the UIExplorer project, I will push my changes as a PR to that.