Show all signature matches when trying to bucket a crash.

[jschwartzentruber]

Searching for matching buckets for an unbucketed crash only shows "good" matches, where "good" is fairly arbitrary. Instead show all matches (ordered by quality of the match), and let the user decide.

[codecov]

Codecov Report

❌ Patch coverage is 5.40541% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.01%. Comparing base (a2d82bf) to head (efd2c59).
⚠️ Report is 498 commits behind head on master.

Files with missing lines	Patch %	Lines
server/crashmanager/views.py	5.40%	35 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #593      +/-   ##
==========================================
- Coverage   66.02%   66.01%   -0.01%     
==========================================
  Files          80       80              
  Lines        7976     7975       -1     
==========================================
- Hits         5266     5265       -1     
  Misses       2710     2710              

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[jschwartzentruber]

@choller pointed out that this was a necessary optimization because for many signatures, searching all buckets would be unacceptably slow.

needs further thought to see if both goals can be achieved. (performant and showing more matches)