Doc updates

Some minor doc updates slated for 0.37.0:

* home: Fix link

* layout-manager: Fix doc string

  This function is private that's no reason to trigger warnings.
  
* build: Add quick-setting-plugins to summary

* docs: Mention .phoshdebug

* docs: Link to more manpages

* docs: Enable fatal warnings during doc build

  This makes sure we no longer ignore links that became stale or
  are mistyped.

We start to fail on gi-docgen warnings to catch new ones fast. Let's see how well this works out.