Change [Tile]EntityRef.dirty to be consistent with all other dirty flags

I don't like how these are all properties. Most of the usages just set dirty=True, and the only time dirty=False is set is when the chunk is written or the scene node is redrawn.

src/mcedit2/editorcommands/find_replace/nbt.py

@@ -519,14 +519,14 @@ class FindReplaceNBT(QtCore.QObject):
                     if tileEntity:
                         tag = tileEntity.raw_tag()
                         _replaceInTag(result, tag)
-                        tileEntity.dirty()
+                        tileEntity.dirty = True
 
                 if result.resultType == result.EntityResult:
                     entity = result.getEntity(self.editorSession.currentDimension)  # xxx put dimension in result!!!!
                     if entity:
                         tag = entity.raw_tag()
                         _replaceInTag(result, tag)
-                        entity.dirty()
+                        entity.dirty = True
 
                 # if result.resultType == result.ItemResult:  # xxx
                 yield

src/mceditlib/anvil/entities.py

@@ -215,8 +215,13 @@ class PCEntityRefBase(object):
 
         return self.__class__(tag)
 
+    @property
     def dirty(self):
-        self.chunk.dirty = True
+        return self.chunk.dirty
+
+    @dirty.setter
+    def dirty(self, value):
+        self.chunk.dirty = value
 
     @property
     def blockTypes(self):
@@ -305,8 +310,13 @@ class PCTileEntityRefBase(object):
 
         return self.__class__(tag)
 
+    @property
     def dirty(self):
-        self.chunk.dirty = True
+        return self.chunk.dirty
+
+    @dirty.setter
+    def dirty(self, value):
+        self.chunk.dirty = value
 
     @property
     def blockTypes(self):