Fix active admin and migrations

So apparently the active admin dashboard is out after 0.6.1, so if you want to use it you have to specify 0.6.0. There were also some duplicate migrations I nuked. If they weren't duplicated, then don't merge this, and we can figure out what was going on with them.

If you do merge this, you will need to run:

```
bundle update
```

to downgrade to 0.6.0 of ActiveAdmin.