contract plugin: add to reports

[derStephan]

Describe the problem

To have an overview of overtimes for many/all users, we now have to open the working time table for each user.

Describe the solution you'd like

There is a report which shows the working times for for all or some users: https://<host>/de/reporting/users/year

It would be perfect to have overtimes and holidays in this report or in another one. If we could export that to excel, it would be great.

Thanks for the plugin. It is working great so far.