Anonym Part 6: Static Pages

[dchukhin]

If this changeset needs to go into the FXC codebase, please add the WMO and FXC label.

This pull request depends on #16965

One-line summary

This pull request makes it possible to create the 'News' and 'Contact' Anonym pages.

Significant changes and points to review

• an abstract AnonymStaticPage that gets subclassed in AnonymNewsPage and AnonymContactPage. Having the pages live in Wagtail (even though they are not editable in Wagtail) allows adding/removing them in the navigation without code changes
• some new logos

Issue / Bugzilla link

Testing

1. log in to Wagtail
2. make sure an Anonym Index Page exists
3. choose to create a child of the Anonym Index Page, and choose an Anonym Contact Page
4. Observe that the page content is not editable, but the page already has content.
5. Go to the Anonym Index Page settings in Wagtail, and add the new page to the navigation.
6. go through steps 3-5 for the Anonym News Page

Note: this pull request does NOT include the styles needed to match the designs

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.79%. Comparing base (0b7d1d9) to head (643100d).

Files with missing lines	Patch %	Lines
bedrock/mozorg/models.py	85.00%	3 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           anonym-part-5-about-page   #16967   +/-   ##
=========================================================
  Coverage                     80.79%   80.79%           
=========================================================
  Files                           164      164           
  Lines                          9365     9384   +19     
=========================================================
+ Hits                           7566     7582   +16     
- Misses                         1799     1802    +3     

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