Blender Git Loki

Outliner: drag&drop - separate moving from parenting

Use drag&drop to parent objects in the outliner by holding down shift.
Previously it was easy to accidently parent objects and there was no way to notice it immediatly.

In some views it is possible to parent objects without using shift; should be obvious from context.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D3812