Make pad & via teardrops 1st-class citizens (props of the pad/via)

Change teardrop generation to rely more heavily on BOARD_CONNECTIVITY
for improved performance.

Add updating of teardrops on BOARD_COMMIT::Push().

Also converts m_CopperItemRTreeCache to std::shared_ptr.
We don't copy it around anyway, and having to create a new set
of std::unique_ptr's for each operation is likely to be more
expensive than std::shared_ptr's overhead.

common/commit.cpp

@@ -194,14 +194,31 @@ CHANGE_TYPE COMMIT::convert( UNDO_REDO aType ) const
         return CHT_REMOVE;
 
     default:
-        assert( false );
-        // Can't fall through if the assert fires, so quiet our warning
-#ifdef NDEBUG
+        wxASSERT( false );
         KI_FALLTHROUGH;
-#endif
 
     case UNDO_REDO::CHANGED:
         return CHT_MODIFY;
     }
 }
 
+
+UNDO_REDO COMMIT::convert( CHANGE_TYPE aType ) const
+{
+    switch( aType )
+    {
+    case CHT_ADD:
+        return UNDO_REDO::NEWITEM;
+
+    case CHT_REMOVE:
+        return UNDO_REDO::DELETED;
+
+    default:
+        wxASSERT( false );
+        KI_FALLTHROUGH;
+
+    case CHT_MODIFY:
+        return UNDO_REDO::CHANGED;
+    }
+}
+