[WIP] estatico-handlebars: Optimize rebuild behavior

[backflip]

Although we have a dependency graph for templates, the rebuilding isn't ideal:

• Let's assume we have a module which is included in many other modules and pages
• We are currently working on this module and viewing its preview page in the browser
• We are editing its template and want to see the result
• However, depending on how the files are streamed through the html build task, we might have to wait for all dependent modules and pages to be rebuilt until our preview page is taken care of

This PR introduces the following changes:

• We keep track of the currently viewed page in the browser
• We prioritize the rebuild of this page by putting it in front of the stream
• We immediately reload the browser when it has been rebuilt
• The remaining modules and pages are rebuilt in the background

[lbsonley]

We are re-activating development on estatico-nou. I am working on a branch to fix the tests so builds pass. If you want this PR merged after the tests are fixed. Please say so. Otherwise it will be closed and the branch will be removed.

Gruess,
Ben

[CLAassistant]

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