When changing an employement profile, recalculate future requests

If you change a users employment profile that defines a different working rota, then any requests made from that point forward should be recalculated based on the new working rota. Example. - User creates request on 1 June for 1 day on 1 July, which equates to 8 hours
- On 14 June, the user is moved to a different employment profile which defines 1 July to only by 7 hours
- System should recalculate the request for 1 July to be 7 hours instead of 8, and update any associated allowance records