Bug 33453: Change the button class of the record cashup modal to btn-primary

Bug 33453: Change the button class of the record cashup modal to btn-primary

To test:

1. Go to System Preferences > find and enable "Use cash registers"
2. Go to Administration > "Cash registers" and create a new cash register
3. Go to Tools > "Transaction history for" > "Record cashup"
4. Click "Record cashup"
5. Modal with change: "Confirm" should be yellow and primary.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>