Fix a couple of issues in dragNodes

Ensure 'this' is related to the object.
Add compatibility with edgequadtree.
Enable drag if graph size=1.
Merge branch 'fix-drag-nodes' into lk-sigma
Update build dragNodes
Prevent 'this' to refer to window
fix gruntfile
Merge remote-tracking branch 'origin/popup' into lk-sigma
Update build plugins.popup