Move update charm to new UX - first iteration

This branch moves the update charm functionality out of the service overview viewlet and into its own viewlet that can be loaded on demand, rather than on opening the inspector.  Note that there are follow-up style branches, and may be follow-up technical branches as well - first iteration.
Given we've checked for `env.setCharm` and told the user it can't be done if `setCharm` doens't exist, shouldn't we execute this in an else so we only bother if `setCharm` *does* exist?