New tutorials

[JelleAalbers]

This adds a trilogy of up-to-date tutorial/howto notebooks for hax. The first two are targeted at new students while the last one may be useful to more seasoned analysts.

I moved the old tutorials into an 'old' folder. All the ones I looked at would no longer work; most of them still reference XENON100 or features that no longer exist or have changed incompatibly. However, some of them are still valuable as documentation for features not described elsewhere. It will take some time to sort these out -- of course input is welcome here.

This also adds a few small things I found useful while writing them:

• hax.cuts.apply_lichen now accepts a deep=True option. This will go one level down the rabbithole of lichens, so you get an elaborate cut report even if you just use a summary lichen such as LowEnergyBackground. See the second tutorial for an example. Also includes a fix for hax.cuts.apply_lichen reports lichen version as nan for some cuts #179.
• hax.runs.get_run_info now accepts pandas series and numpy arrays of run number/names, rather than just lists and tuples.
• Added a small helper function hax.runs.tags_count that counts how often a tag occurs in a selected dataframe of datasets. Again an example is in the second tutorial.

After this is merged, we can advertise the tutorials on the README page and in the analysis guide on the wiki.

[tunnell]

I flipped through the examples. They look really nice and informative. I'd just delete the old ones (it's why we have version control) since I think they're more confusing than not. We also have SR1Results and other repositories that people can copy-paste from.

[tunnell]

I think these look really good. I'd just drop the old notebooks that we made since they are confusing.

[feigaodm]

wow, I took a look at the new tutorials and they look very good.

[JelleAalbers]

Thanks guys, I now removed the old tutorials from XENON100 and others for which I was certain they wouldn't work anymore. There's one or two that are worth keeping and will probably still run, or maybe only with minor modifications.

I updated the README to link to these tutorials; once this is merged I'll add them to the analysis/beginners guide on the wiki.