HTML code for head of frozen world

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**What would you like to achieve?**
I want to add external script tags to the `` of a frozen world. I know that I can do it with `loadViaScript`, but Google is fussy about multiple loads of the chart loader so I want to do it statically in a `script` tag in `head`. As I read the code in
```
$world.execCommand("open browser", {moduleName: "studio/ui.cp.js", packageName: "engageLively--galyleo-dashboard", codeEntity: [{"name":"GalyleoStudioWorld","type":"class-decl"},{"name":"__head_html__","type":"class-instance-getter"}]});
```
it seemed the way to do this was in the `__head_html__` property of the world object, but that code isn't showing up in the built page. So I assume the freezer code has changed since this code was written, so my question is simple: where do I put HTML code that goes into the header. I can always just hand-edit the built `index.html`, but what a kludge.

**How are you trying to achieve that**

**Alternative solutions**
If applicable, what other solutions have you tried?

**Additional Resources**
Please provide links to any custom code that might be necessary to grasp your problem. Screenshots of custom component, etc. are also appreciated.

**Version**: Please paste the lively.next commit on which the problem occurred here (use the copy button of the Version Checker in the bottom left corner).
c725a776b26bd744331765a4881ba4c0557d2fea

Start with the GalyleoStudioWorld __head_html__ class-instance-getter in studio/ui.cp.js and compare its output with the generated index.html from a frozen world. Trace the freezer path to determine where head HTML is assembled; done means external script tags appear in the generated page without hand-editing index.html.

Written by the indexing model from the issue text.