Add Visit classes to the pointsprite namespace.

By moving all the visit classes to a namespace that is unique
to the plugin, we can remove the duplicate symbols between
these classes and VisItBridge which also has these classes.

Change-Id: I888a00ad8119681f36d777158ec2d816f4bdc54a
PointSprite and VisItBridge can exist together in static builds

Change-Id: I3c350e644e73541e97f67647c66a0e87cb522a45
Merge topic 'duplicate_visit_symbols' into next

e82bdfd PointSprite and VisItBridge can exist together in static builds
6711dcc Add Visit classes to the pointsprite namespace.