Update travis environment to xenial [ci skip]

Manually set c++11 compiler is not g++ >= 6

clang++ doesn't still defaults to c++98 or c++03. Thanks to Sergey Alirzaev
for pointing that out.

Send qlite return code to DEBUG log.

Make it compile with dcmtk > 20170228 Closes: #32

The newDicomElement functions were moved into DcmItem and are now
exposed as static methods. Test for this with CMake and if the new version
is found, forward the calls to newDicomElement to DcmItem::newDicomElement.

Currect shader call and prepare new release. Closes: #18

Remove some code that is not used and bump version

Make yet another release. Closes: #18

The shadder code using the if-statement did not compile with the
Intel shader compiler, but using "clamp" corrected the problem.

Update Changelog

New release.

New release to fix PACS communication regression