Added 'disableSelectStartList' to disable select start on certain items

[davemckenna01]

Hi, I love your package. I wanted my selectables to be draggable without having to disable the SelectableGroup (to get selectable and draggable behaviour like the files/folders in an OS GUI like Windows/Mac etc). To achieve this I sort of mimicked how you implemented the ignore list. So with this PR, if you try to start a lasso drag on a selectable item that has a certain class, you won't be able to.

If you like this addition feel free to merge it. If you need anything else from me, like code convention clean up, testing, anything at all, let me know.

Again, thanks for your package.

[vercel]

This pull request is being automatically deployed with ZEIT Now (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://zeit.co/skymk1/react-selectable-fast/3g5njhfco
✅ Preview: https://react-selectable-fa-git-fork-davemckenna01-disable-selec-8e2808.skymk1.now.sh

[ghost]

Any status of getting this in? I'm very interested in this functionality!