adding import of filter top and bottom

[luitjansl]

Fixes #1053

Description

On importing wells, the filter top and bottom are now parsed and stored in the project file data structure

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