Remove dependency to Immutable.js

[jorilallo]

I started experimenting with this library as it essentially offers exactly what I need. Could you consider removing Immutable.js as a dependency given that it's not really needed but and should be up to the consumer of the library to opt-in? Looking at my webpack stats, it seems to add 139KB which is non-trivial given that it's adding no benefit for me.

[magnushiie]

This was a hard choice I had to make during the initial design of the component - the initial use case where this component is used in our (internal) application uses Immutable.js heavily, and I didn't want to lose performance by making a copy of the data structures for handing it to the treeview component. Immutable.js also gives a nice API to manipulate immutable collections.

I anticipated the potential consumers of this API that didn't want to use Immutable.js but couldn't figure out a great solution to handle both cases well. We'll keep this issue open, but don't plan to removing the dependency just yet.

[jorilallo]

I understand. I did write a version without just to realize that I'm ok with simpler version so didn't end up using it. It's cool project still, I hope you guys end up polishing it more and consider a little leaner public release