Calculate correct position for tips with position:fixed; style

Changes;
- [x] Calculate correct position for tips with position:fixed; style.
- [x] Look at per-tip settings for scroll, to allow scrolling to select tips.

Also, please correct `v2.1` tag. It must be called `v2.1.0` to be used by bower!
```bash
git tag v2.1.0 v2.1
git push origin v2.1.0
```