Drag and drop enhancements

Drag and drop enhancements

- Add support for DROP_LINK
- Add rename prompt on name collision with automatic name resolution
- Add support for unknown trace type icon
- Fix propagation of selected trace type to experiment traces
- Updated user guide

Change-Id: I1eb7c7bcbe5566a0fc507aef1554780515d62eb5
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/10667
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bhufmann@gmail.com>
IP-Clean: Bernd Hufmann <bhufmann@gmail.com>
Tested-by: Bernd Hufmann <bhufmann@gmail.com>