Log message cleanup
Slightly improved, but still far from complete handling of clipping and clipGroups; LayerGroup.visit always visits in index order
Disable "Image Assets" menu if no documents are open.

To accomplish this, switch from using currentDocumentChanged events
to imageChanged events to see when the set of open documents changed.

Also, clarify (hopefully) some of the logic around updateOpenDocuments.
Report error to user if final asset path length exceeds the platform maximum
Merge pull request #208 from adobe-photoshop/jrb/iwehrman-v2-with-menu-disablement

Disable "Image Assets" menu if no documents are open
Correctly scale approximate bounds
Disable SVG asset generation by default
Merge branch 'iwehrman/v2' into ps-next