Consider phasing out various custom-searches

There are several custom-searches. I'm sometimes confused by the behavior with them -- and generally feel suspicious because (a) they don't have much test coverage and (b) they involve lots of edge-cases/combinations and (c) they're not very visible to users (ie not much foot-traffic), (d) I sort think they were written quickly a long time ago, and (e) there's overlap with reporting.

It would be useful to re-evaluate each of them and perhaps phase-out some. For example, a phase-out might look like this:

1. Create a new extension
2. Move the search(es) to the extension
3. Bundle the extension with the main tarball
4. Disable by default
5. Add an upgrade message telling people how to get them back
6. Test the upgrade/transition process to ensure it works

NOTE: Take care when disabling/re-enabling. There might be references to the searches in various places (e.g. smart-group definition; custom navigation), and you want the old IDs/URLs to continue work.