Better scrolling management when the component gets focus.

- Make sure the component will not be covered by keyboards. 
- Each of individual component might have different distance from the keyboard.
- Measurement taken is now relative to the keyboard, rather than some arbitrary numbers `topPadding`.
Merge commit '410d0fa9cb32d9b861a540b25d26b43a85db378a' into lweform-scrolling
Merge pull request #19 from moneytree/lweform-scrolling

Better scrolling management when the component gets focus