Pluggable invoice transmission methods (#5020)

* Flexible invoice transmission

* UI work

* Add peppol and output

* API support

* Profile integration

* Simplify form for individuals

* Remove sent_to_customer usage

* more steps

* Revert "Bank transfer: Allow to send the invoice direclty to the accounting department (#2975)"

This reverts commit cea6c340be.

* minor fixes

* Fixes after rebase

* update stati

* Backend view

* Transmit and show status

* status, retransmission

* API retransmission

* More fields

* API docs

* Plugin docs

* Update migration

* Add missing license headers

* Remove dead code, fix current tests

* Run isort

* Update regex

* Rebase migration

* Fix migration

* Add tests, fix bugs

* Rebase migration

* Apply suggestion from @luelista

Co-authored-by: luelista <weller@rami.io>

* Apply suggestion from @luelista

Co-authored-by: luelista <weller@rami.io>

* Apply suggestion from @luelista

Co-authored-by: luelista <weller@rami.io>

* Apply suggestion from @luelista

Co-authored-by: luelista <weller@rami.io>

* Apply suggestion from @luelista

Co-authored-by: luelista <weller@rami.io>

* Make migration reversible

* Add TransmissionType.enforce_transmission

* Fix registries API usage after rebase

* Remove code I forgot to delete

* Update transmission status display depending on type

* Add testmode_supported

* Update src/pretix/static/pretixbase/js/addressform.js

Co-authored-by: luelista <weller@rami.io>

* Update src/pretix/static/pretixbase/js/addressform.js

Co-authored-by: luelista <weller@rami.io>

* Update src/pretix/static/pretixbase/js/addressform.js

Co-authored-by: luelista <weller@rami.io>

* New mechanism for non-required invoice forms

* Update src/pretix/base/invoicing/transmission.py

Co-authored-by: luelista <weller@rami.io>

* Declare testmode_supported for email

* Make transmission_email_other an implementation detail

* Fix failing tests and add new ones

* Update src/pretix/base/services/invoices.py

Co-authored-by: luelista <weller@rami.io>

* Add emails to email history

* Fix comma error

* More generic default email text

* Cleanup

* Remove "email invoices" button and refine logic

* Rebase migration

* Fix edge case

---------

Co-authored-by: luelista <weller@rami.io>

src/pretix/plugins/banktransfer/urls.py

@@ -19,19 +19,13 @@
 # You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
 # <https://www.gnu.org/licenses/>.
 #
-from django.urls import include, re_path
+from django.urls import re_path
 
 from pretix.api.urls import orga_router
 from pretix.plugins.banktransfer.api import BankImportJobViewSet
 
 from . import views
 
-event_patterns = [
-    re_path(r'^banktransfer/', include([
-        re_path(r'^(?P<order>[^/][^w]+)/(?P<secret>[A-Za-z0-9]+)/mail-invoice/$', views.SendInvoiceMailView.as_view(), name='mail_invoice'),
-    ])),
-]
-
 urlpatterns = [
     re_path(r'^control/organizer/(?P<organizer>[^/]+)/banktransfer/import/',
             views.OrganizerImportView.as_view(),