Bindable Items should support Livedata

[Nattle]

Thanks for the amazing library it's my goto default in all my projects.

I was hoping to improve support for LiveData withing BindableItems. It's a simple ~1 line fix. It sould be correct in all cases as well and not degrade performance if LiveData is not used. I can open a pull request but I wanted to get your thoughts first since there are two ways to go about it:

Here's the commit with the proposed changes. Option #1 is what I'm proposing. Option 2 is left just in case you can see an issue with option 1, though I think it clutters the API.
https://github.com/Nattle/groupie/commit/f2abd9e27ca789c19d2eda78c6aabcb7629f9e1a