Updated `learn/Interactive-UI-Elements.elm` for 0.14 (for issue #201)

Hi,

This version of `learn/Interactive-UI-Elements.elm` compiles with version 0.14, and I updated the contents to the best of my knowledge (I only spent a few hours reading about Elm).

So please proofread :)

Hopefully it fixes #201.

Cheers!
Sébastien.