Allow state value to be changed externally after the initial value

[abobwhite]

I have been burned by this several times now where I need to bind the value (state) passed into the slate-editor to a changed prop than what it was initialized with but slate-editor never looks at that value except upon initial creation. In my situation, I'm changing locales in my UI to bind to the different translated values. It appears that slate itself doesn't restrict this but slate-editor never exposes a way to externally change the state value.

Let me know if you need any more details.