Fix ghost relations.

This branch fixes the following issues:
- the ghost relation line disappears right after creating
  the relation: that was due to ecs functions mutating the
  relation data;
- the ghost relation is now a grey line with hollow circle;
- the relation line now follows the service blocks when they
  are moved.

In my external monitor some more contrast between the
relation color and the background could help. Luca and
Spencer are working on that.

QA:
- make devel;
- go to `http://<GUIURL>/:flags:/mv/il/`;
- drag mysql, click deploy and close the inspector;
- do the same with wordpress;
- connect the two services;
- the grey relation should be displayed;
- move the two uncommited services, the relation line
  should be updated correctly;
- click deploy on the status bar,
  the services are now deployed.

Please also ensure relations still works without the flags.