Scaleup UI polish.
Display constraints correctly in summary panel.
Merge pull request #436 from huwshimi/scaleup-polish

Scaleup UI polish

This branch fixes the scale up button colour and sets the unit count from the model.
Merge pull request #433 from huwshimi/fix-blank-constraints-message

Display constraints correctly in summary panel

If the constraints are set to null then we should display the correct message. See: https://bugs.launchpad.net/juju-gui/+bug/1339782