Implement MxAtomId and reference counter (stl set) (#109)

* Implement MxAtomId and reference counter (stl set)
* Partial success in hiding 4786 warning spam.
* Build out most of MxOmni::Destroy since it also touches the set

* Add some size asserts

LEGO1/mxatomidcounter.cpp

@@ -0,0 +1,18 @@
+#include "mxatomidcounter.h"
+#include "decomp.h"
+
+DECOMP_SIZE_ASSERT(MxAtomIdCounter, 0x14);
+DECOMP_SIZE_ASSERT(MxAtomIdCounterSet, 0x10);
+
+// OFFSET: LEGO1 0x100ad7f0
+void MxAtomIdCounter::Inc()
+{
+  m_value++;
+}
+
+// OFFSET: LEGO1 0x100ad800
+void MxAtomIdCounter::Dec()
+{
+  if (m_value)
+    m_value--;
+}