Found this while debugging.
The `hasCalendarURL` function does a check if the url is in the config.
But the calendar sees only his own config part, so this check is always
true (tested with more than one calendar module in `config.js`).
Since the project's inception, I've missed a clear separation between
default and third-party modules.
This increases complexity within the project (exclude `modules`, but not
`modules/default`), but the mixed use is particularly problematic in
Docker setups.
Therefore, with this pull request, I'm moving the default modules to a
different directory.
~~I've chosen `default/modules`, but I'm not bothered about it;
`defaultmodules` or something similar would work just as well.~~
Changed to `defaultmodules`.
Let me know if there's a majority in favor of this change.
