Allow overriding of password validation

[paltman]

This closes #141. Applied manually because of rebase hell after such a long period. Thanks @rizumu

[codecov]

Codecov Report

Merging #361 (ccb0402) into master (e9a6053) will increase coverage by 0.15%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #361      +/-   ##
==========================================
+ Coverage   72.57%   72.73%   +0.15%     
==========================================
  Files          22       22              
  Lines        1393     1401       +8     
  Branches      171      170       -1     
==========================================
+ Hits         1011     1019       +8     
- Misses        307      308       +1     
+ Partials       75       74       -1     

Impacted Files	Coverage Δ
account/hooks.py	77.77% <66.66%> (-1.39%)	⬇️
account/forms.py	71.96% <100.00%> (+1.96%)	⬆️

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