Add rerender event to all image loads in MWExtensioNode.
MWHieroNode's implementation of onParseSuccess is now the same as
its parent so can be deleted.
Change-Id: Iaa4999372f1ba88a7bdf1490fc3f8640af77ceae
Mostly as a demonstration of how easy this is with MWExtensionNode.
The icon was chosen with the following criteria:
1. Recognisable (the ankh is quite common in popular culture, right?)
2. Doesn't look idiotic to academics (I've consulted an Egyptology
PhD and they can confirm it's not the glyph for penis)
3. Renders well at <16x16
That said it does look a little like a stick man...
Bug: 43118
Change-Id: I9f9e8af501401866bfeecf0eec3690a705fbd4db
