Update code to use our models.

:warning: **Not yet ready to be merged** :warning:

- [ ] Update search code to use `Party` and `Song` model.
- [x] Update party controller to use `Party` and `Song` model.
- [x] Remove old code from party controller.
- [ ] Verify that the party controller changes actually works. @kloek could you please have a look at that?


Get this branch by doing;
```Shell
git pull
git checkout --track origin/feature/use-our-models
```

And to get back to the master branch do `git checkout master`.