This option provides a more convenient way to overlay dummy packages.
It also adds a function `config.lib.test.mkStubPackage` that can,
e.g., be used for `package` options.
* neomutt: Fix eval error when primary account not enabled
If neomutt is enabled for an account, but not the primary account, the
configuration will fail with "list index 0 is out of bounds".
This adds the first neomutt-enabled account as a fallback.
* neomutt: add regression test/update tests