ENH: add constructors from UList<Point> + FixedList<label,..>

- simplifies construction from edge,triFace etc.

This is to access the face/edge/point status of the nearest at the
same time to ensure a consistent result.

Using getVolumeType query in distanceSurface, not simple normal
dot-product comparison, fails on edges.

Squashed merge of particleInteractions up to
commit e7cb5bcf0315c359539ef1e715e1d51991343391

triangle, from:

http://en.wikipedia.org/wiki/Inertia_tensor_of_triangle

Adding the ability to calculate the inertia tensor of a polygon face
by summing the triangle inertias.

Added a test application to draw a test face with its principal
axes and moments of inertia.

the include file back to mathematicalConstants.H to make upgrading code slightly easier.