Export sum of weights

[sauloperez]

Closes #87 . It does so by passing in the type of export to perform. That type is used in the job class to choose which query object and serializer pair is used. That's what changes between the two different results views.

The routes follow the same approach we adopted for the results pages. A controller (and endpoint) for each view.

[codecov-commenter]

Codecov Report

Merging #99 (8970e4e) into master (997c1f8) will increase coverage by 0.35%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
+ Coverage   94.07%   94.43%   +0.35%     
==========================================
  Files          54       58       +4     
  Lines         726      772      +46     
==========================================
+ Hits          683      729      +46     
  Misses         43       43              

Impacted Files	Coverage Δ
...ecidim/action_delegator/admin/create_delegation.rb	96.15% <ø> (ø)
...elegator/admin/consultations/exports_controller.rb	100.00% <100.00%> (ø)
...legator/admin/exports/sum_of_weights_controller.rb	100.00% <100.00%> (ø)
...legator/admin/results/sum_of_weights_controller.rb	100.00% <100.00%> (ø)
...ction_delegator/export_consultation_results_job.rb	100.00% <100.00%> (ø)
...cidim/action_delegator/sum_of_membership_weight.rb	100.00% <100.00%> (ø)
...queries/decidim/action_delegator/sum_of_weights.rb	100.00% <100.00%> (ø)
...ueries/decidim/action_delegator/type_and_weight.rb	100.00% <100.00%> (ø)
...idim/action_delegator/sum_of_weights_serializer.rb	100.00% <100.00%> (ø)
lib/decidim/action_delegator/admin_engine.rb	100.00% <100.00%> (ø)
... and 4 more

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