Lib agnostic styling

[Hideman85]

I've seen in the issues that the goal at the end of this project is to provide a full out of box editor ready to use on top of Slate. One great feature would be to have way to be able to already implement some styling but in a provider way.

Let's take a example, in my react app I use AntDesign as CSS lib and there is already design for Tooltip and Modal the things is the BallonToolbar provide a new Tooltip design. Since we are using React we could be able to pass the component in the config for using it internally. This is same for Modals like inputting the link properties (displayText, url) could be done by a modal.

But to avoid to reinvent styling for tooltip and modals it could be great to have a provider pattern so we can use either AntDesign, MaterialUI, BootStrap or whatever library with ease. And maybe later we can see some repo like slate-plugins-antd that is on top of this one and provide the needed configuration for having a consistent styling.

[zbeyens]

At the moment, everything is stylable by using the styles option (or props for components like BalloonToolbar) or by using the class names. Your suggestion is interesting so we have a centralized place for styling, that can be implemented on top of the existing styles option. In the meantime, using the class names is a centralized workaround.

[zbeyens]

Let's track this in #363