Allow employee to add sickness to the planner themselves Merged

In previous systems, our employees have been able to log their sickness themselves and then managers are notified of when this has been added.

For our company this would be important to have as the majority of our employees work remote and them having to alert a manager or HR and then for them to enter on their behalf is likely to lead to occasions of sickness not being tracked if managers are busy or HR aren't made aware.