Presentations, now with admin py

![presentations_adminpy-2](https://f.cloud.github.com/assets/320464/2276763/9feef420-9f37-11e3-81c8-f26f0a884468.png)

This is nice - the only problem that I'm on the fence about is that an individual Presentation page takes a long time to generate because of the database hits, to wit:

```
SELECT `data_record`.`id`, `data_record`.`created`, `data_record`.`modified`, `data_record`.`name`, `data_record`.`parent_id`, `data_record`.`source`, `data_record`.`manager`, `data_record`.`next_update`, `data_record`.`owner_id` FROM `data_record` 
```

takes 1653.24ms per slide... (in debug mode anyway)