ENH: Add pointlist support to OpenIGTLinkIF and fix warnings

Fixes #3077
Fixes #3248

Co-authored-by: Isaiah Norton <inorton@bwh.harvard.edu>

From: Junichi Tokuda <tokuda@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22242 3bd1e089-480b-0410-8dfb-8563597acbee