Change all of the SelectSingle CFs to dropdowns

This makes the UI tighter and friendlier in general.
We still run into issues because EditConstituency overrides the
appearance of the CF.
Upgrade existing select singles in older RTIRs to use dropdowns
Don't hardcode Rows => 1

In b48d9816 this one view of incident editing/creation silently switched
to having Constituency be a dropdown.  It didn't change any of the other
places you can change constituency on IR/Incident/Investigation.
Port in the smallest possible part of EditCustomFieldSelect

This doesn't bring in any of the category support because the code in
here is so far out of wack with core that it's basically a total redo.

This really just need to become an External Custom Field.
Merge branch '2.9/cf-tweaks' into 2.9-trunk

Conflicts:
	etc/upgrade/3.0.0rc2/content
Fix up the MANIFEST

We moved a number of docs around and didn't fix it
Clean up our doc links

Some of these went to docs/ some still to lib.
Assume we'll be able to link to bestpractical.com when this ships.