(#29) Initial multiple selection.
(#29) Implemented multiple selection, multiple delete (still buggy).
(#29) Fixed deletion of multiple nodes at once.
(#29) Dragging multiple nodes for multiple selection.
(#29) Highlight links connecting selected nodes.
(#29) Auto layout of selected nodes.
(#29): Fix link handling on multiple selection. Changelog.
Merge branch 'feature/29-multiple-selection'