Add scroll bars

I will rebase this branch more than once. Be carefull if you merge this PR.

Remaining tasks:
- [ ] Update README minSdkVersion = 5
- [ ] Enable scrollbars only if they are needed.
- [ ] ScrollBar inside the content. Image 1
- [ ] Overlap the scrollbars. Image 2

![device-2013-10-20-000321](https://f.cloud.github.com/assets/721244/1367223/7780ca06-390a-11e3-80b4-48353388bbcd.png)

![device-2013-10-20-000306](https://f.cloud.github.com/assets/721244/1367222/7185fdb0-390a-11e3-9fee-437843deec1b.png)