No id columns required on the Sample/Prep templates

Fixes #404 
There's a convenience `tolist` method that pandas provides and according to `%timeit` is also a bit faster:

```python
In [7]: %timeit df.index.tolist()
100000 loops, best of 3: 3.71 µs per loop

In [8]: %timeit list(df.index)
100000 loops, best of 3: 4.56 µs per loop
```