[RFC] admin: prefetch related fields

[blueyed]

This only does it for the customer's changelist view now, but it meant
to be generic enough for other admins.

You can easily see the number of queries going down when using django-debug-toolbar or something similar.

TODO:

• tests

[paltman]

I'm a 👍 on this. Can you please use double-quotes is all that I ask, please?

[blueyed]

double-quotes

Sure. At least you do not have two-space indendation.. ;)

I have some stashed tests to test the number of queries in existing tests - will update.

[blueyed]

Tests have been added - but there might be a better way.

[codecov]

Codecov Report

Merging #366 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #366      +/-   ##
=========================================
+ Coverage   99.39%   99.4%   +<.01%     
=========================================
  Files          34      34              
  Lines        1662    1676      +14     
  Branches      135     138       +3     
=========================================
+ Hits         1652    1666      +14     
  Misses          5       5              
  Partials        5       5

Flag	Coverage Δ
#py27dj110	99.4% <100%> (ø)	⬆️
#py27dj111	99.4% <100%> (ø)	⬆️
#py27dj18	99.4% <100%> (ø)	⬆️
#py34dj110	99.4% <100%> (ø)	⬆️
#py34dj111	99.4% <100%> (ø)	⬆️
#py34dj18	99.4% <100%> (ø)	⬆️
#py34dj20	99.4% <100%> (ø)	⬆️
#py35dj110	99.4% <100%> (ø)	⬆️
#py35dj111	99.4% <100%> (ø)	⬆️
#py35dj18	99.4% <100%> (ø)	⬆️
#py35dj20	99.4% <100%> (ø)	⬆️
#py36dj111	99.4% <100%> (ø)	⬆️
#py36dj20	99.4% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
pinax/stripe/admin.py	100% <100%> (ø)	⬆️

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[blueyed]

Would like some feedback on the tests.
@ticosax @paltman @lukeburden