Multichannel Timeseries: don't rely on custom downloads

[maximlt]

For reasons unrelated to examples.holoviz.org (see #418 (comment)), @droumis has implemented inlined downloads (via pooch) on top of anaconda-project downloads for the Multichannel Timeseries example. I would prefer not to include that sort of code, we cannot guarantee users they will be able to run the notebooks in any other way than via anaconda-project. It's not that I have a passion for this tool, it's just that this whole project is too big to offer custom runtime for each and every example.

[droumis]

Multichannel Timeseries: don't rely on custom downloads #448

I don't think this title is a fair assessment of the situation. The example does not "rely" on custom downloads. Before this issue was created, the example was already using anaconda-project for all the data downloads. The only extra layer is that in the notebook, there is a check if the data is downloaded to the location that anaconda-project should download the data to, and if the data is not present, it uses pooch to do so.

[droumis]

My solution ensures that a user does not require anaconda-project, but anaconda-project is still the encouraged method of running the project, per the website's instructions.