Shading: Add more operators to Vector Math node.

Add Multiply, Divide, Project, Reflect, Distance, Length, Scale, Snap,
Floor, Ceil, Modulo, Fraction, Absolute, Minimum, and Maximum operators
to the Vector Math node. The Value output has been removed from operators
whose output is a vector, and the other way around. All of those removals
has been handled properly in versioning code.

The patch doesn't include tests for the new operators. Tests will be added
in a later patch.

Reviewers: brecht, JacquesLucke

Differential Revision: https://developer.blender.org/D5523