[Partners] Partner's logos are positioned by last edited and not position

[tudoramariei]

Describe the bug
When adding a partner logo, the user can specify a position (the position in the list). The logos are positioned in the order of the last edit.

To Reproduce
Steps to reproduce the behavior:

1. Go to /admin/partners logged in as an admin
2. Add three partners, with positions 1, 3, and 2 (in order of creation)
3. Open the front page and look at the logos
4. The logos are positioned in the order they were added (1, 3, 2)
5. Return to the menu and edit the first logo (modify website, name, etc.)
6. Open the front page and look at the logos
7. The logos are positioned in the order they were last edited (3, 1, 2)

Expected behavior
The logos should always be positioned in the order of their position.
Logos without a position should be placed after the logos with a specified position in the last edited order.

Screenshots
Expected order: Code4, CT911, Commit
Actual order: Code4, Commit, CT911 (in the order they were last edited)

Additional context
Related to #431