Update pydata-sphinx-theme?

[jonnew]

This is a copy of this issue: open-ephys/ONI#72

Currently we have pydata-sphinx-theme fixed at version 0.13.3. However, they have released version 0.16.1, which seems to come with some good quality of life improvements. Unless there is a reason for maintaining this version, we should consider updating to the most recent version, and even change the Pipfile so that it not fixed but always pull the most recent version (i.e., pydata-sphinx-theme = "*").

If we want to do this, we should standardize the other docs as well, I know that at least one other doc site (miniscope-docs) uses the most recent version of pydata-sphinx-theme, but others (e.g., acq-board-docs) are still fixed at version 0.13.3.

[jsiegle]

The main reason for pinning the version is that various customizations we've made are not guaranteed to work after upgrading. I agree we should upgrade to 0.16.1, but not specifying the theme version in the template is risky (and also means we may end up with differences across docs sites).

We will update the gui-docs site to 0.16.1 prior to the release of GUI v1.0; that would be a good time to upgrade the rest of the docs sites as well.