feat(operations): a job's error and warning show in the reader's language

A job stored its error and its result's warning as English text, much
of it built with the values in it (volume paths, a disk, libvirt's
error), so no catalog could translate it, and the job pages and panel
showed English whatever the language.

A job now stores them as messages: our English text, marked for
translation, and its values; libvirt's own text is a message without
values and is shown as it is. The jobs API and pages put them in the
reader's language. OperationError keeps its text and values apart for
the same reason, so a refusal raised while a job is submitted is shown
translated too. Messages one after another still read as sentences.

Errors stored before are kept as one message each, shown as they were.

operations/views.py

@@ -14,6 +14,7 @@ from vrtManager.util import OperationError
 from . import jobs as jobs_module
 from .api.serializers import OperationSerializer
 from .models import Operation, last_seen
+from .utils import said, words
 
 
 def _visible(user):
@@ -71,7 +72,7 @@ def cancel(request, pk):
     try:
         jobs_module.cancel(op.pk, request.user)
     except OperationError as err:
-        messages.error(request, str(err))
+        messages.error(request, words(said(err)))
     return redirect("operations:job", pk=op.pk)
 
 
@@ -83,5 +84,5 @@ def resolve(request, pk):
     try:
         jobs_module.resolve(op.pk, request.user, request.POST.get("outcome", ""), request.POST.get("note", ""))
     except OperationError as err:
-        messages.error(request, str(err))
+        messages.error(request, words(said(err)))
     return redirect("operations:job", pk=op.pk)