[READY] Drop bottle in favour of a tiny hand-rolled "framework"

[bstaletic]

Turns out ycmd needs a tiny part of the whole framework specification from PEP 3333. Note that this does not fully conform to the specification, but it mostly does.

Currently we are only handling POST and GET requests. Support for middleware is limited. Inspired by Bottle plugins API, but only plugin.__call__ and app.install are implemented. Error handling is also limited. Application needs to replace the default error handler that will handle all errors.

However, this just about fits ycmd's needs.

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This change is 

[codecov[bot]]

Codecov Report

Merging #1736 (c00691f) into master (1693a93) will increase coverage by 0.02%. The diff coverage is 97.19%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1736      +/-   ##
==========================================
+ Coverage   95.46%   95.48%   +0.02%     
==========================================
  Files          83       84       +1     
  Lines        8201     8311     +110     
  Branches      163      163              
==========================================
+ Hits         7829     7936     +107     
- Misses        322      325       +3     
  Partials       50       50              

[bstaletic]

All review comments have been addressed. Ycmd and YCM tests are passing and a manual test with unicode identifiers passed as well. Merging.