Improve date input of positions

[Andreas]

Is your feature request related to a problem? Please describe.
Currently, the date inputs of positions (start and end) can be any value.

Describe the solution you'd like
Add the following constraints

• End date must not be before start date
• Changing the start date should automatically change the end date too (while keeping the times the same difference)

Describe alternatives you've considered
None

Additional context