Merge pull request #91 from chrisshayan/Release9

Release9 is live now on http://techlooper.navigosgroup.com:8080/techlooper/index.html
Use Optional as JDK 8 supports us
Merge commit '1a9a5e1f6326c3ab47a1748241de3f38561d319c'
Merge commit '63fa78be1acad71c57956ea30bb730937bfec950'
Apply stream API to histogramEnums
Refactor com.techlooper.service.impl.VietnamWorksJobStatisticService#countJobsBySkill
Change some function names in com.techlooper.service.impl.VietnamWorksJobStatisticService