Add a way to track organizer issues

[amakarudze]

Every now and then community members report issues to do with Django Girls workshop organizers through email. However, since email is separate from the CMS, these issues fall through the cracks and are only uncovered when the same organizer has another issue reported against them.

This pull request introduces:

• An OrganizerIssue model to track issues to do with organizers.
• Adds a field is_blacklisted to the user model.
• Adds status of organizer being blacklisted to the string representation of user to make it easy for Awesomeness Ambassador to know when an organizer has been blacklisted.
• Also add checks when new event application is received to see if any of the listed organizers are blacklisted.
• Adds a field to event application admin to easily show this to Awesomeness Ambassador.
• Tests for these changes [TO DO].

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (6a05d70) 81.01% compared to head (e57bc27) 81.24%.
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #939      +/-   ##
==========================================
+ Coverage   81.01%   81.24%   +0.23%     
==========================================
  Files          95       98       +3     
  Lines        2860     2938      +78     
  Branches      269      271       +2     
==========================================
+ Hits         2317     2387      +70     
- Misses        492      499       +7     
- Partials       51       52       +1     

Files	Coverage Δ
core/admin/__init__.py	100.00% <100.00%> (ø)
core/admin/forms/organizerissue.py	100.00% <100.00%> (ø)
core/admin/organizerissue.py	100.00% <100.00%> (ø)
core/admin/user.py	63.63% <ø> (ø)
core/models/organizerissue.py	100.00% <100.00%> (ø)
core/models/user.py	100.00% <100.00%> (ø)
organize/admin.py	60.00% <ø> (ø)
organize/models.py	91.42% <88.88%> (-0.24%)	⬇️
organize/views.py	63.15% <12.50%> (-8.28%)	⬇️

... and 4 files with indirect coverage changes

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[marksweb]

Think this looks good with those improvements in 👍