Shading: Refactor Math node and use dynamic inputs.

- Implement dynamic inputs. The second input is now unavailable in single
operand math operators.
- Reimplemenet the clamp option using graph expansion for Cycles.
- Clean up code and unify naming between Blender and Cycles.
- Remove unused code.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D5481

intern/cycles/blender/blender_shader.cpp

@@ -326,10 +326,10 @@ static ShaderNode *add_node(Scene *scene,
   }
   else if (b_node.is_a(&RNA_ShaderNodeMath)) {
     BL::ShaderNodeMath b_math_node(b_node);
-    MathNode *math = new MathNode();
-    math->type = (NodeMath)b_math_node.operation();
-    math->use_clamp = b_math_node.use_clamp();
-    node = math;
+    MathNode *math_node = new MathNode();
+    math_node->type = (NodeMathType)b_math_node.operation();
+    math_node->use_clamp = b_math_node.use_clamp();
+    node = math_node;
   }
   else if (b_node.is_a(&RNA_ShaderNodeVectorMath)) {
     BL::ShaderNodeVectorMath b_vector_math_node(b_node);