Add Jenkinsfile for CI and fix for consecutive messages

[praetp]

I noticed consecutive consumer callbacks would still see old messages as well.
If the producer sends 'A', 'B', 'C', the consumer would receive

• 'A'
• 'A', 'B'
• 'A', 'B', 'C'

[codecov]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is 77.77%.

@@            Coverage Diff            @@
##             master      #14   +/-   ##
=========================================
  Coverage     89.72%   89.72%           
  Complexity       70       70           
=========================================
  Files            10       10           
  Lines           185      185           
  Branches         20       20           
=========================================
  Hits            166      166           
  Misses           11       11           
  Partials          8        8

Impacted Files	Coverage Δ	Complexity Δ
...ertx/ext/web/handler/sse/impl/EventSourceImpl.java	91.22% <77.77%> (ø)	18 <0> (ø)	⬇️

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[aesteve]

Hello and thanks a lot for your work.

I'm so sorry I missed your PR. Since I never noticed issue with SSE on the server, I forgot about it.
I didn't even pay attention your PR was about the client, not the server.

Once again, thanks a lot for your work. I'm going to merge it, then delete the Jenkinsfile since the project is using travis and not Jenkins, but nevermind, thanks a lot for your interest and your work.