Update cmake logic to build vtkMap library, & renamed example app

Builds shared object by default
Changed main.cpp --> example.cpp
Changed vtkMap exe to example
Add vtkOsmLayer to TestMapClustering & wsmap applications
Add vtkInteractorStyleMap

* Use left-click to pan
* Zoom 2x each mouse-wheel click
Update zoom logic to center on mouse coordinates

Translate camera along vector from camera to zoom point
Increase resolution of cluster marker (sphere), for aesthetics
Change cursor to "hand" when panning.

To match google maps
Fix "hand" cursor to "sizeall", update zoom-out to use mouse position.
Fix uninitialized variable
Merge pull request #43 from OpenGeoscience/john/lib-and-interactor

John/lib and interactor