Improved the "Blocked Logins" page's admin integration

[ataylor32]

This is useful for things such as a customized site_title and/or site_header, for example.

[kencochrane]

LGTM

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (a972dae) 92.78% compared to head (3834873) 92.58%.
Report is 2 commits behind head on master.

Files	Patch %	Lines
defender/views.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #239      +/-   ##
==========================================
- Coverage   92.78%   92.58%   -0.21%     
==========================================
  Files          13       13              
  Lines         416      418       +2     
==========================================
+ Hits          386      387       +1     
- Misses         30       31       +1     

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