Issue #961 flow packages from imod5

[luitjansl]

Fixes #961

Description

implements importing from a imod5 project file for storage and initial conditions.

Checklist

• [X] Links to correct issue
• [ ] Update changelog, if changes affect users
• [X] PR title starts with Issue #nr, e.g. Issue #737
• [X] Unit tests were added
• [ ] If feature added: Added/extended example