[WIP] Bounded Binding: Remove old bind strategy

This guy will need #1534 to go in (I've opened it with respect to that #1547, but will
reopen with respect to `lift_30` once everything goes in). It will also require that we
deprecate the appropriate stuff in 2.6 (something we hadn't undertaken yet).

The PR blows away `bind` and most things that came with it. It preserves a few functions
that were in `BindHelpers` that were related to more general HTML manipulation, which
now live in an `HtmlHelpers` trait instead. It also rearranges the `ToCssBindPromoter`
implicits so that they are implicit classes and in a single centralized place (a
`CssBindImplicits` trait). These are mixed into `HtmlHelpers` and through there into
`Helpers`, so importing `Helpers._` will continue to import the appropriate implicit
conversions.

The second thing this does is rewrite a couple of points where we were still leaning on
the old binding strategy, particularly `PaginatorSnippet` and the `Menu` snippet. The
snippets themselves may not be optimal now; however, I made the rewriting function
very similarly to how it functioned before (using CSS classes instead of the element
names that the binding style was using), leaving decisions on whether the snippets
should be further reworked for another time.

`lift-webkit` still does not compile due to `LiftScreen`. We discussed promoting
`CssBoundLiftScreen`'s binding implementation to be the main `LiftScreen` one in
[this mailing list discussion](https://groups.google.com/d/msg/liftweb/v7gzlnKMSoM/IspntBkMXdgJ), but I think that work is maybe best for @pbrant if he
has the time and is willing?

Done/pending work:
 - [x] Remove `BindHelpers` and `BindHelpersSpec`
 - [x] Move still-used generic stuff to `HtmlHelpers`
 - [x] Preserve `BindHelpersSpec`s for `HtmlHelpers` stuff in `HtmlHelpersSpec`
 - [x] Port snippets still using `bind` to CSS selector transforms
 - [x] Put implicits for `ToCssBindPromoter` in a common place
 - [ ] Ensure untested stuff in `HtmlHelpers` is tested
 - [ ] Make `LiftScreen` compile without `bind`
 - [ ] Make sure all specs are passing once `LiftScreen` is compiling