- Move UI code out of ExtensionManagerView into ExtensionManager
- Properly escape extension description after toggling truncated part
Fix: toggling Extension Manager long/short description would always show
the string for the installed version of an extension (if installed), even
when looking at the Available tab. Use info from the current view-model
rather than making absolute references to ExtensionManager's model.

Also, use $.data() instead of $.attr("data-...").
Merge pull request #9018 from adobe/pflynn/extmanager-truncation-cleanup

Clean up how Extension Manager handles long descriptions