Fix incorrect types for <GiftedChat /> component

[danilvalov]

Please check this PR carefully. I'm not 100% sure about it because I don't fully understand the original typing logic that was there before (I think the old logic was wrong from the start).

My research started with trying to understand why the renderFooter prop in the <GiftedChat /> component gives me a typescript error if I try to use an argument from the renderFooter function. I found it weird that we extend the GiftedChatProps interface from the MessageContainer class and not from the MessageContainerProps interface. This is a problem why Typescript told me that this function had no arguments, although the function itself returned props (this function refers to the MessageContainer class, not the MessageContainerProps interface).

And in the end I noticed this pull request. There are several users discussing this issue.

I think my PR will fix all the major typing issues. But I don't understand why no one noticed this elephant in the code before me.