Motion > metadata > submission date: even without date the heading is visible for 'normal' users

[MSoeb]

Describe the bug
If no date has been entered under 'Submission date', the term 'Submission date' is still visible for all users which can see motions. This is unnecessary.

How to Reproduce
Steps to reproduce the behavior:

1. open a meeting
2. open motions > create a motion. Delete the submission date after motion create.
3. open participants > create a user as delegate with the permission to see motions
4. login as delegate and check the motion detail view metadata.

Expected behavior

Additional context
If no date has been entered under 'Submission date', the term 'Submission date' should be hidden for all users who do not have the permissions ' Can manage motions' and 'Can manage motion metadata'.