Moved content of inst/extdata to the pRolocdata dataverse

[lgatto]

As of version 1.43.1, the content of inst/extdata (except for the README file) had been moved to a dedicated pRolocdata dataverse. I have created a first dataset containing all files as of version 1.42.0 (and 1.43.0).

I have used my institution's dataverse because (1) zenodo didn't allow to upload > 100 files (we had 142) and (2) the dataverse allows to add different datasets under the same umbrella.

In the future, I suggest we

1. systematically archive new dataset files on a server (the dataverse above or elsewhere).
2. Add the link and any additional information (such as the original source of the data) in inst/extdata/README.

Ping @lmsimp @Charl-Hutchings

[lmsimp]

This sounds like a reasonable plan 👍

[lgatto]

There is however an issue with the README file. Il looks it hasn't been updated since 2018, despite new datasets being added.