[ML] inline normEuklid().
[ML] Add VecNormType enum.

This is required when specifying norm in Petsc vector interface.
Merge pull request #342 from norihiro-w/modify-VectorNorm

add VecNormType
add MathLib/Nonlinear in CMakeLists.txt
- move VecNormType to LinAlgEnums.h
- extend norm functions
add Picard class
add tests for Picard