Deprecate xbind-related things in Mapper.

This includes a bunch of field binding and form snippet
helpers. New versions are added for doing similar things with
CssSels instead.
Fix a broken interpolation fix.

I was using string interpolation, but that doesn't work in 2.9.2, so I
"fixed" it, but I really didn't, but now it's fixed :p
Merge pull request #1546 from lift/deprecate-xbind-stuff

2.6: Deprecate xbind-related things in Mapper.

This includes a bunch of field binding and form snippet helpers. New versions
are added for doing similar things with CssSels instead.

They don't map 1-to-1 because CSS selector transforms don't support namespaces,
amongst other things. Transforms are combined using andThen in case they match
the same element or match a parent element and something else needs to affect
the child.