Added ability to parse javascript getters and convert them into dart getters.

Also applied this to all core elements so you can see the changes.
minor style suggestion: consider merging both branches?

```
} else {
   var p = current.properties[name];
   if (p == null) p = current.properties[name] = new Property(name, '');
   if (m.group(3) == 'get') p.hasGetter = true;
   if (m.group(5) == 'get') p.hasSetter = true;
```