Use Django's import_string so as to avoid re-implementing it

[jdufresne]

No description provided.

[codecov]

Codecov Report

Merging #913 into master will increase coverage by 0.3%.

@@            Coverage Diff            @@
##           master     #913     +/-   ##
=========================================
+ Coverage   76.82%   77.12%   +0.3%     
=========================================
  Files          30       30             
  Lines        1661     1644     -17     
  Branches      246      245      -1     
=========================================
- Hits         1276     1268      -8     
+ Misses        311      303      -8     
+ Partials       74       73      -1

Impacted Files	Coverage Δ
debug_toolbar/toolbar.py	79.71% <100%> (+3.8%)	✅
debug_toolbar/panels/signals.py	76.59% <33.33%> (+4.59%)	✅

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[matthiask]

Thanks! I just checked whether import_string is documented, and indeed it is.