Bug 24786: Update paycollect to use session register

Bug 24786: Update paycollect to use session register

This patch adds handling to allow for the use of the session cash
register by default if it has been set, otherwise it defaults to '--
None --' and requires the end user to select the register to proceed
with the payment.

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>