Remove BindHelpers and BindPlus for HtmlHelpers.

HtmlHelpers keeps just the bare minimum of non-old-bind-
related functionality from BindHelpers, things related directly
to manipulating NodeSeqs rather than to bindings.

Note that while util compiles, webkit emphatically does not.
Work is forthcoming to fix that.
Restore scaladoc to Bindable trait.
Bring back AttrHelper.

This is used fairly extensively in S, and isn’t directly tied to
the old binding approach.
Turn ToCssBindPromoter to implicit classes.

Before, we had a couple of implicit conversions from String to
ToCssBindPromoter, which was a final case class. We now
have a CssBindImplicits trait that defines a CssBindPromoter
class and two implicit classes that extend it, one for strings
and one for CssSelector instances.

These implicits are mixed into HtmlHelpers so they are
available, as before, when Helpers._ is imported.
Fix a higherKinds warning.

Also add a FIXME to verify whether the higher kinded
AttrHelper type parameter is needed.
Move lift:embed to CSS selector transforms.

It now operates on ids, not lift:bind-at elements.
Restore stripHead in HtmlHelpers.
Strip bind helper methods from CometActor.
Fix a lost implicit Str->JsExp conversion.

Presumably this was indirecting through a BindHelpers implicit
and ending up as a JsExp somehow…
Reimplement Menu.group using CssSel.
Change Menu.group to return a CssSel.

Since we’re yielding a top-level CssSel, this lets folks decide
whether to combine using & or andThen when referencing the
snippet directly.
Reimplement PaginatorSnippet.paginate using CssSel.

Also SortedPaginatorSnippet’s override of .paginate.
Restore find(Box|Option|Id) to HtmlHelpers.

These are generic HTML helpers rather than relying on
anything binding-related, and they’re used in other places in
the codebase.
Restore deepEnsureUniqueId to HtmlHelpers.

Also unify most of its implementation with that of
ensureUniqueId.
Remove lift:bind support in LiftSession.
Preserve applicable BindHelpersSpecs.

These are now in an HtmlHelpersSpec singleton.
BindHelpersSpec goes away completely.
Fix CssSelectorSpec for lost BindHelpers.

We now import all of Helpers, which provides the appropriate
implicits and such.
Rearrange HtmlHelpersSpec to match source order.
Add spec for HtmlHelpers#findId.
Add spec for HtmlHelpers#removeAttribute.