Instead of returning zero euro when the value isn't assigned we now return the correct value null. This makes money field return the correct value and makes it obvious when there is a null value.
This approach is needed to fit the requirements of the ticket 374.

A new field is added to the PersonEntity, which will be used for a feature in the future. This will allow to set a defaultDailyRate for the person.
This new field needs a database migration, which is also integrated.

This feature lets the user add a default daily rate to each person. According to this default daily rate the missing rates can be automatically be assigned with this rate.
This avoids that the user needs to add each missing rate manually.

Budgets in different projects can have the same name, so looking it up
by name could return more than one result. To fix this we need to look
the budgets up with their id.

When the user adds records manually the automatic feature will potentially overwrite already created records.
That's why the feature is disabled when the user adds a record manually.