Allow employees to request TOIL to be added to their balance

At present if an employee works overtime or additional hours the manager has to manually add the TOIL by going into settings on the planner.

It would be useful if there was a mechanism for the employee to request the additional hours be added to their TOIL balance when TOIL is accrued in a similar way to a holiday request, so that when the manager approves the request it adds to their balance automatically (or if it's declined not add the hours and notify the employee of the reasons for the request being declined)