set_context function

seaborn has a nice way to set the plot styling for a particular context (like figures for a talk, poster, paper or notebook)

I was thinking we could take a similar approach with superEEG, setting a context to run the code on a single computer, cluster, or some other setups. I idea would be to:

```
import superEEG
superEEG.set_context('google-cluster')
```

This would change an internal config object that determines the behavior of our functions (how the jobs are split up etc). thoughts?