Move Max/Min from SGVector to CMath

Agreed. Moving methods one-by-one eases review. However, pushing all commits here does not sound that good (it actually sounds kind of the contradictory to moving methods one-by-one).

I just meant you could move the unit tests of the methods you have moved from SGVector to CMath from SGVector_unittest to Math_unittest (or whatever the unit test file for CMath is called :-)