Bug 11975: improve the batch patron deletion code

Bug 11975: improve the batch patron deletion code

This patch tries to improve the code for the cleanborrowers.pl tool.

- use KohaDates plugin and Koha::DateUtils for date management,
  removing a dependency on C4::Dates
- replace variables step1, step2 and step3 with step
- add a JavaScript check if no action if checked

Test plan:
- Backup your DB
- Play with the Patron deletion/anonymisation tool and try to find
  something inconsistent.
If you don't find something different, it works!

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>