It's more convenient to manage notification channels separately, as it
is done with email settings. Notification hook and other forms are
adopted to only select channels. Hooks can now use more than one
channel.
- Adopted postcss and tailwind config to new version
- renamed colors bluegray->slate etc to not have custom
definitions (hope to reduce migration next time)
- tailwind now doesn't build the complete css anymore, so the
`dev-ui-build` script must compile both
This is a start to have different kinds of notifications. It is
possible to be notified via e-mail, matrix or gotify. It also extends
the current "periodic query" for due items by allowing notification
over different channels. A "generic periodic query" variant is added
as well.
