Improvements on ScrollPanel, CellList and minor issues

[apanizo]

Trying to split the commit in three different pull requests not sure what short key I used in my browser but it sent the pull request with all my commits.

I think there are no important changes, so if you do not want some of them, just let me know and I dig in rebase and cherry pick for doing it properly.

Basically there are two features:

• CellList: Including methods for rendering one T in one position, avoiding rendering the whole list.
• ScrollPanel: Two new events, when the panel has just bounced and when the panel is close to bounce (we are using this for doing easily a continuous scroll).

If you need more info, just let me know.

Sorry about not delivering several pull requests, I thought gitHub allows to select commits when sending them (in the future I'll do correctly :D).