Output precision change

Get clang version in CMake

add a new file conversion tool VTK2OGS

Update for clang compiler.

Corrections based on clang warnings

Extend MathLib linear algebra objects.

This a lightweight pack-unpack class holding two vectors.

This helps with generalization when using essentially same concept of addition.

This simplifies matrix construction in many places because in many cases we need just a bilinear form.