Enable shipkit release publishing

[cgtz]

• Set up the shipkit (https://github.com/mockito/shipkit/blob/master/docs/getting-started.md) gradle plugin for publishing releases to bintray.
• Configure travis to automaticly generate github releases and maven artifacts when PRs are merged to the master branch.

Tested locally using ./gradlew testRelease
I have set up travis-ci environment variables to use my bintray/github account/api keys.

[codecov-io]

Codecov Report

Merging #1239 into master will decrease coverage by 13.62%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             master    #1239       +/-   ##
=============================================
- Coverage     85.84%   72.22%   -13.63%     
- Complexity       76     6043     +5967     
=============================================
  Files             9      439      +430     
  Lines           544    34913    +34369     
  Branches         56     4430     +4374     
=============================================
+ Hits            467    25216    +24749     
- Misses           58     8551     +8493     
- Partials         19     1146     +1127

Impacted Files	Coverage Δ	Complexity Δ
...ava/com.github.ambry/config/PerformanceConfig.java	100% <0%> (ø)	4% <0%> (?)
...main/java/com.github.ambry.cloud/CloudReplica.java	73.91% <0%> (ø)	8% <0%> (?)
...m.github.ambry.replication/ReplicationMetrics.java	94.92% <0%> (ø)	43% <0%> (?)
...ava/com.github.ambry/frontend/SecurityService.java	100% <0%> (ø)	4% <0%> (?)
...b.ambry.cloud/CloudBlobCryptoAgentFactoryImpl.java	81.81% <0%> (ø)	2% <0%> (?)
...ain/java/com.github.ambry/frontend/Operations.java	0% <0%> (ø)	0% <0%> (?)
...n/java/com.github.ambry.clustermap/Datacenter.java	88.7% <0%> (ø)	26% <0%> (?)
...github.ambry.messageformat/TtlUpdateSubRecord.java	100% <0%> (ø)	2% <0%> (?)
...in/java/com.github.ambry.cloud/CloudFindToken.java	33.33% <0%> (ø)	7% <0%> (?)
...i/src/main/java/com.github.ambry/network/Port.java	57.14% <0%> (ø)	5% <0%> (?)
... and 420 more

---

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[lightningrob]

It will be great to link the published javadoc to the main README.ml page

[mockitoguy]

This looks good. Thank you!