add email settings api, add notifications email settings to webinterface

internal/config/config.go

internal/db/dbmigrate/scripts/v0.10.0.pre.sql

internal/db/dbrepo/userrepo/users.go

internal/endpoints/consent/pkg/capability.go

internal/endpoints/notification/calendar/calendar.go

internal/endpoints/settings/email/email.go

internal/mailing/mailing.go

internal/mailing/mailtemplates/mailtemplates.go

...mailing/mailtemplates/templates/verify_mail.html.mustache

.../mailing/mailtemplates/templates/verify_mail.txt.mustache

internal/mytoken/event/pkg/event.go

internal/server/api.go

internal/server/web/partials/scripts.mustache

...server/web/partials/settings-notifications-email.mustache

internal/server/web/partials/settings-notifications.mustache

internal/server/web/sites/settings.mustache

internal/server/web/static/js/settings-notifications.js