ulyanov_et_al_2016 replication stylization and small fixes

[codecov[bot]]

Codecov Report

Merging #249 (c78a089) into master (7ba28c6) will decrease coverage by 0.0%. The diff coverage is 100.0%.

@@           Coverage Diff            @@
##           master    #249     +/-   ##
========================================
- Coverage    98.6%   98.6%   -0.1%     
========================================
  Files          39      39             
  Lines        1558    1557      -1     
========================================
- Hits         1537    1536      -1     
  Misses         21      21             

Impacted Files	Coverage Δ
pystiche_papers/ulyanov_et_al_2016/_data.py	100.0% <100.0%> (ø)
pystiche_papers/ulyanov_et_al_2016/_loss.py	100.0% <100.0%> (ø)
pystiche_papers/ulyanov_et_al_2016/_modules.py	100.0% <100.0%> (ø)
pystiche_papers/ulyanov_et_al_2016/_nst.py	95.4% <100.0%> (+0.1%)	:arrow_up:
pystiche_papers/li_wand_2016/_utils.py	96.1% <0.0%> (ø)
pystiche_papers/gatys_et_al_2017/_utils.py	100.0% <0.0%> (ø)
pystiche_papers/gatys_ecker_bethge_2016/_utils.py	100.0% <0.0%> (ø)

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[jbueltemeier]

Splitted into #251, #252, #253, #255 and #256.