Improve time tracking overview

[knollengewaechs]

URL of deployed dev instance (used for testing):

• https://timetrackingexpandtable.webknossos.xyz/

Steps to test:

• Make sure to have some tracked times in explorative annotations and tasks
• log in as admin-user and go to "Time tracking overview" through navbar
• query time tracking entries
• expand details for users
• test download buttons
• test as non-priviledged user (should only see yourself)
• test without login (view shouldn't be accessible)

TODOs:

• [x] see issue
• [x] think about csv export structure
• [x] fix types
• [x] adjust tests to new param: getTimeTrackingForUserSpans, getTimeTrackingForUser
• [x] fix that non-admin user cannot see themselves because "page doesnt exist"
• [x] fix that expendable button is in wrong position after adjusting filters
• [x] make sure new project line looks good with segmentation stats

Issues:

• fixes #7708

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(Please delete unneeded items, merge only when none are left open)

• [x] Updated changelog
• [x] Removed dev-only changes like prints and application.conf edits
• [x] Considered common edge cases

[knollengewaechs]

wouldn't unix timestamps make more sense as they are easier to parse? not sure whether they are coming from back-end or front-end...

I had added them in the frontend in the first place, but changed them to unix timestamp now :)

[knollengewaechs]

no worries, thanks for looking into it! I will merge it on monday then :)