Updated Service, Method, Message Identifiers to be CamelCased

[waveywaves]

The incompatibility caused between the generated .pb.gw.go
and .pb.go files due to inconsistent identifier capitalization
has been fixed here.

Logic from protoc-gen-go for the Message, Service and Method
Names is ported to protoc-gen-grpc-gateway.

Have made changes in the template.go file and have written a
test so we don't regress this in the future.

This fixes #683

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[codecov-io]

Codecov Report

Merging #866 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #866      +/-   ##
==========================================
+ Coverage   52.95%   52.99%   +0.03%     
==========================================
  Files          39       39              
  Lines        3907     3910       +3     
==========================================
+ Hits         2069     2072       +3     
  Misses       1642     1642              
  Partials      196      196

Impacted Files	Coverage Δ
protoc-gen-grpc-gateway/gengateway/template.go	65.51% <100%> (+1.23%)	⬆️

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[achew22]

Thanks so much for the PR! Do you think you could add a test that verifies this behavior so we don't accidentally regress in the future?

[waveywaves]

@achew22 Yes, I'll add a commit for the test in the PR. Thanks for checking.

[waveywaves]

Thanks so much for the PR! Do you think you could add a test that verifies this behavior so we don't accidentally regress in the future?

I have added the test and updated the PR

[johanbrandhorst]

LGTM

[johanbrandhorst]

Thanks for your contribution!