Tidy up rails integration

[st0012]

This is to make different steps of integrations more understandable.

[codecov-io]

Codecov Report

Merging #1150 (460ff62) into master (87c03f0) will increase coverage by 0.25%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1150      +/-   ##
==========================================
+ Coverage   97.76%   98.01%   +0.25%     
==========================================
  Files         188       28     -160     
  Lines        7867      706    -7161     
==========================================
- Hits         7691      692    -6999     
+ Misses        176       14     -162     

Impacted Files	Coverage Δ
sentry-rails/lib/sentry/rails/railtie.rb	88.46% <100.00%> (+3.46%)	⬆️
sentry-raven/lib/raven/instance.rb
...-sidekiq/spec/sentry/sidekiq/error_handler_spec.rb
...en/spec/raven/integrations/rails/activejob_spec.rb
sentry-raven/spec/raven/integrations/rails_spec.rb
...-ruby/spec/sentry/transport/http_transport_spec.rb
...ations/rails/overrides/debug_exceptions_catcher.rb
sentry-ruby/lib/sentry/interfaces/request.rb
sentry-ruby/lib/sentry/rack/interface.rb
sentry-raven/lib/raven/logger.rb
... and 151 more

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