Bug 18630: Translatability (Clubs): 'Cancel' is ambiguous and leads to mistakes

Bug 18630: Translatability (Clubs): 'Cancel' is ambiguous and leads to mistakes

The button to cancel a club enrollement is labelled with 'Cancel'. That is ambiguous and translates e.g. in German to 'Abbrechen' which can lead to
mistakes.

To test:
- Apply patch
- Enroll a patron to a club
- Enable public enrollment in OPAC
- Verify that the button to cancel enrollment in both OPAC and staff client
  reads 'Cancel enrollement' (instead of 'Cancel' without patch)
  (The button appears on the patron's detail pages in OPAC and staff client)

Amended for comment #4 / mv

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>