Added iScroll 5 typings

iScroll version 5 changed it's object name from iScroll to IScroll.
To prevent breaking builds for other people (still on v4) I thought it would be best to add a new file and leave the old one untouched.
I have not yet fully checked all the options, but plan to do so this week, and update with a new pull request when I have.
I also plan on adding some documentation/intellisence, also for the version 4 typings.