Store rounded participation score in database

[Ninjaclasher]

Fixes #1595.

[codecov-commenter]

Codecov Report

Merging #1725 (cd422b0) into master (36ea904) will increase coverage by 0.04%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #1725      +/-   ##
==========================================
+ Coverage   46.38%   46.43%   +0.04%     
==========================================
  Files         217      218       +1     
  Lines       12386    12416      +30     
==========================================
+ Hits         5745     5765      +20     
- Misses       6641     6651      +10     

Impacted Files	Coverage Δ
judge/contest_format/atcoder.py	32.30% <0.00%> (ø)
judge/contest_format/ecoo.py	31.81% <0.00%> (ø)
judge/contest_format/icpc.py	29.72% <0.00%> (ø)
judge/contest_format/ioi.py	27.77% <0.00%> (ø)
judge/contest_format/legacy_ioi.py	37.03% <0.00%> (ø)
judge/views/two_factor.py	39.75% <ø> (+0.70%)	⬆️
judge/signals.py	64.19% <20.00%> (-2.91%)	⬇️
judge/admin/profile.py	62.22% <87.50%> (+1.98%)	⬆️
judge/contest_format/default.py	84.44% <100.00%> (ø)
judge/models/profile.py	90.90% <100.00%> (-0.71%)	⬇️
... and 8 more

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[kiritofeng]

LGTM; only remaining question is if it's worth it to run this computation against all currently existing participations for consistency.