Add remove relation functionality to ecs

Relations can now be removed from the environment using the ecs system for deployed or ghost relations. There is a known bug with this which will be resolved as a follow-up: https://bugs.launchpad.net/juju-gui/+bug/1333395
One thought: it's more verbose, but if you coded it up this way, it would be more grep-friendly (grep 'window\.flags\.mv') for removal on down the road:

~~~~
window.flags = {};
window.flags.mv = true;
~~~~