Node merging

![screen shot 2013-10-02 at 7 51 28 pm](https://f.cloud.github.com/assets/58878/1259856/29a0ddc0-2bfa-11e3-9abe-28b30e134f62.png)

- [x] Button UI
- [x] Button data attributes
- [ ] Filter relevant tags only
- [ ] Delete osm_id in OSMChange
- [ ] tag conflict modal
- [ ] append relevant tags to existing tags
- [ ] removeLayer when done