Setup and tear down actions.

Need to implement the following:
@qdev-dk/qcodes should there be the .run() in the following snippet ?

``` python
qc.Measure(vna.s11, vna.s21).setup(..).teardown(..).run(..)
```

See #263 for more info qc.Measure (not yet implemented).

``` python
Loop(..).setup(..).teardown(..).run(..)

```

Start by reading issue #263, then compare the proposed qc.Measure and Loop setup/teardown/run snippets to understand the intended measurement API. The work is done when the lifecycle behavior and whether run belongs in the chain are defined and implemented for the referenced use cases.

Written by the indexing model from the issue text.