Style the upgrade charm panel and link

Styled the upgrade charm panel.

The close button does not currently work as we do not store the inspector state. There's a card to rectify this.

The header with the close button should not be included in the scrolled area, but the solution to fix this requires the viewlet to have destroy called on it when the panel is closed. There is a card to fix this also.

QA:
- drag a charm to the canvas
- click deploy and confirm
- click on the service block to open the inspector
- click "Change version" in the inspector
- it should be styled the same as the "Change version" section on this mockup: https://docs.google.com/a/canonical.com/file/d/0B7XG_QBXNwY1MlRWZlNQN214WGc/edit