Add algorithm for concave annular endcapping.

Initially based on annular endcapping code, this algorithm
builds a closed loop polygon from the inner and outer edges
by adding an artificial edge between them.

It then uses vtkPolygon to mesh the non-convex polygon,
and removes the artificial edge to complete the triangulation.
Add concaveannular endcaps mode to vmtksurfacecapper.

Also fix some inconsistent whitespace in this file.
Add concaveannular endcaps option to meshgenerator, and option to skip remeshing.
Merge pull request #71 from martinal/martinal/concaveannularendcapping

Add algorithm for concave annular endcapping. 
Great, thanks!