Clarifying the documentation of ScatterLayout

The previous documentation was based in the old RelativeLayout (based in a Scatter). The documentation didn't indicate the difference between Scatter and ScatterLayout. It is also more clear if we compare the ScatterLayout against the RelativeLayout since they behaviour is the same (except for the scatter functionality). Scatter is already relative so the only difference that I can see is the possibility of using the hint properties.
Merge pull request #1331 from robertour/master

Updating ScatterLayout documentation (ScatterLayout vs Scatter and ScatterLayout vs FloatLayout)