HttpClient5 support

[Amy Nguyen]

Hello, my company is currently using olingo for Java. Our organization's policy 
considers httpclient 4.5.14 to be EOL because it has not been updated in almost 
3 years and has a more active replacement library with httpclient5. Are there 
any plans for olingo to move from httpclient to httpclient5? Is that something 
that you would be open to us possibly contributing to the next release?