Code review comment for lp://staging/~djsiegel-deactivatedaccount/do/trunk

This branch fixes a lot of the little implicit text item quirks. I've localized the addition of the ImplicitTextItem to search results in UniverseManager.Search. I've also overridden PassesTypeFilter in ProxyElement so SelectTextItem appears as an ITextItem in the second pane again. All of this code will be rewritten for 0.9.

This branch also seeks to address the issues we've had with SelectedTextItem by introducing Services.Application.Summoned to allow plugins to receive a main-thread notification when summon occurs. SelectedTextItems uses this event to read the clipboard at a safe time. However, it's not all that simple -- sometimes we still seem to lock up, even on the main thread.

Please test this branch extensively. Use modifier items, use actions that return results, etc.