First draft for release news 1.7.

CHANGELOG

+BornAgain-1.7
+  > Summary:
+    1) We moved the source repository from our own server to GitHub,
+         https://github.com/scgmlz/BornAgain.
+       This makes it easy for external contributors to propose changes in form of pull requests.
+       Appveyor and Travis continuous integration server automatize tests.
+       Python usage examples are now also covered by tests.
+    2) GUI support for fitting ... masking ...
+       Control parameters for different fit engines unified ...?
+    3) Behind the scenes: many directories, files, classes renamed or reorganized.
+
 BornAgain-1.6.2, released 2016.07.15
   > Hotfix:
   * Bug #1558: Memory leakages in Python on Simulation::getIntensityData call