Calculate math classes from outputs, not inputs.

It's important to get spacing right that the domTree classes reflect
math atom types. So use those types exclusively, rather than
repeating the type mapping twice (once when building spans, once in
getTypeOfGroup).

* Remove getTypeOfGroup.
* Add getTypeOfDomTree (simpler).
* Adjust supsub type calculation.
* Adjust delimsizing internals.

test/katex-spec.js

@@ -883,8 +883,8 @@ describe("A delimiter sizing parser", function() {
         var leftParse = getParsed(normalDelim)[0];
         var rightParse = getParsed(bigDelim)[0];
 
-        expect(leftParse.value.delimType).toEqual("open");
-        expect(rightParse.value.delimType).toEqual("close");
+        expect(leftParse.value.mclass).toEqual("mopen");
+        expect(rightParse.value.mclass).toEqual("mclose");
     });
 
     it("should parse the correct size delimiter", function() {