Add data to existing map

[IanMayo]

I'd like us to make the "Create Data View" process more realistic.

So, at the end, instead of creating the empty Data View window, instead we add the cluster layer to the existing map.

I'll change the walkthrough so that we do "Add to existing" instaed of "Create new Data View".

Hopefully you can retrieve the map view, in order to create the cluster, and add it to the map view control.

[Morphexe]

I commited this with another issue with map.
#72 handles all this and the other map related issue.