Added namespaced way to refer to types in schemas.

Also made proper namespacing work for enums.

You can now say namespace.MyTable as the type when declaring
a field that refers to a type in a different namespace.

Previously, it would work just referring to MyTable, however
with the recent commit fixing namespaced types this now
is ambiguous.

Change-Id: Ieaa3f4ac1662b8c4dc1f16e1898ea3cdb02e10fd
Tested: on Linux.

tests/monster_test.fbs

@@ -39,7 +39,7 @@ table Monster {
   /// multiline too
   testarrayoftables:[Monster] (id: 11);
   testarrayofstring:[string] (id: 10);
-  enemy:Monster (id:12);
+  enemy:MyGame.Example.Monster (id:12);  // Test referring by full namespace.
   test:Any (id: 8);
   test4:[Test] (id: 9);
   testnestedflatbuffer:[ubyte] (id:13, nested_flatbuffer: "Monster");