admin: display created and modified fields

[PetrDlouhy]

Proposed changes

I just wanted to display created and modified fields in admin to make it easier to debug potential problems.

Types of changes

Please check the type of change your PR introduces:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (PEP8, lint, formatting, renaming, etc)
• Refactoring (no functional changes, no api changes)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Build related changes (build process, tests runner, etc)
• Other (please describe):

Checklist

• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

Don't think tests are needed for this, but I might try to add some if required.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (07da4af) 94.11% compared to head (d7f9613) 94.12%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #514   +/-   ##
=======================================
  Coverage   94.11%   94.12%           
=======================================
  Files          39       39           
  Lines        1139     1140    +1     
  Branches      133      133           
=======================================
+ Hits         1072     1073    +1     
  Misses         43       43           
  Partials       24       24           

Flag	Coverage Δ
unittests	94.12% <100.00%> (+<0.01%)	⬆️

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Files	Coverage Δ
social_django/admin.py	97.05% <100.00%> (+0.08%)	⬆️

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[nijel]

Merged, thanks for your contribution!