Update camera on vtkMap::ShowArea(), if renderer has been initialized.

Also:
* Changed code to keep Center coordinates in lat-lon
* Set zoom 1 level lower (undo last iteration)
Merge pull request #58 from OpenGeoscience/john/extend-visibility

Separate layer visibility from feature visibility.
vtkFeatures now properly delete their vtkLayer.
Pass and Return by const where it makes sense.
Properly delete all vtk objects when vtkMap is deleted.

vtkMap never properly deleted any feature or layer.
Merge pull request #62 from robertmaynard/stopVTKLeaks

Properly delete all vtk objects when vtkMap is deleted.
Merge branch 'master' into john/show-area
Prune conus bounds a bit, so that default display has 1 marker  & 1 cluster
Merge branch 'john/show-area' into databrowser

Resolved conflicts:
	vtkMap.cxx
Merge pull request #63 from robertmaynard/const_char_pointers

LGTM
Merge branch 'master' into databrowser