`repetitions` and `barsperrepeat` fields on CRS and CDS accept invalid input

Sentry Issue: STRATHSPEY-Y

ValueError: invalid literal for int() with base 10: '2x40'
  File "django/db/models/fields/__init__.py", line 2055, in get_prep_value
    return int(value)

ValueError: Field 'repetitions' expected a number but got '2x40'.
(12 additional frame(s) were not displayed)
...
  File "ace4/db/views/search.py", line 409, in form_valid
    recordings = recordings.filter(**{key: reps})