update theme plugins for 3.4

[kaitlinnewson]

Update theme plugins:

• Classic
• Health Sciences
• Immersion
• Pragma

[kaitlinnewson]

@asmecher Ready for a review

[asmecher]

Thanks, @kaitlinnewson! The plugin validation tool only expects one new plugin per PR (another thing that could be improved), so it only validated classic. Could you split this into several PRs, one per plugin?

Also, I suspect it's only cosmetic, but I do see a bunch of warnings in the extraction part of the test:

tar: Ignoring unknown extended header keyword 'LIBARCHIVE.xattr.com.apple.quarantine'
tar: Ignoring unknown extended header keyword 'LIBARCHIVE.xattr.com.apple.provenance'

This appears to be due to differences between BST tar and GNU tar; it might be worth using GNU tar on your system to build plugins. On the extraction side, adding --warning=no-unknown-keyword seems to silence it, but I'd hate to start spreading that around everywhere in case it has knock-on effects.

[kaitlinnewson]

@asmecher new PRs created and I've recreated the release packages using GNU tar.

[asmecher]

All merged, thanks, @kaitlinnewson!