Make Touchable* tappable again

[TimBroddin]

I noticed two problems with Touchable* not being tappable:

• There was no zIndex on the active slide (so you got transparant slides in front)
• The panresponder stole all use interactions

Made a quick fix. Also changed the name of the NPM package (because you get a 404 when trying to install the scoped package).

Thanks for this nice piece of code guys

[TimBroddin]

I added another commit to this pull request on accident. It does this:

• pass onboarding prop to the child containers (so you can access parent component)
• add two new methods: previous() & next(). So now you can go the next screen programmatically (through the onboarding prop).