Improve issue search

[ethantkoenig]

Make improvements to issue search: (see #530 (review))

• Add support for searching comment contents
• Add unicode normalization and tokenization
• Move indexer specific code out of models and into a separate module (where it can potentially be reused in the future)
• Update bleve dependency
• Add integration tests for issue search

Don't let the big add/removal figures scare you; that's because of the updated dependency

[lunny]

It seems new issue on sqlite wasn't indexed.

[ethantkoenig]

@lunny Fixed

[codecov-io]

Codecov Report

Merging #2387 into master will increase coverage by 0.1%.
The diff coverage is 30%.

@@            Coverage Diff            @@
##           master    #2387     +/-   ##
=========================================
+ Coverage   26.86%   26.96%   +0.1%     
=========================================
  Files          84       84             
  Lines       16936    16906     -30     
=========================================
+ Hits         4550     4559      +9     
+ Misses      11712    11672     -40     
- Partials      674      675      +1

Impacted Files	Coverage Δ
models/pull.go	20.2% <0%> (-0.06%)	⬇️
models/issue_indexer.go	9.67% <17.64%> (+6.13%)	⬆️
models/issue_comment.go	31.1% <21.05%> (-0.42%)	⬇️
models/issue.go	24.95% <73.33%> (+0.3%)	⬆️

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[lunny]

LGTM

[lafriks]

Do not use same path for mysql, pgsql and sqlite as they will conflict when run in parallel

[ethantkoenig]

@lafriks Good catch, fixed

[lafriks]

Would be great if these directories would also be added to make clean but otherwise LGTM

[lafriks]

make LG-TM work