README: Add image and link with build status
DOM: Delete on*() methods
Aggregate: Merge filter*() implementations

This also fixes some issues in filter().
Change semantics for links to routes

By providing an implicit for ``InstantiatedRoute``, it is now more generic.
To link to a route, write:

HTML.Link(Routes.route())("Caption")
Widget: Poll in withCSS()
Bootstrap: Deal with ``active`` flag more consistently
Widget: Fix bug in withCSS()

withCSS() may be called multiple times.
README: Add links to similar projects
Bootstrap: Fix regression
HTML: Enforce return type in List.bind()
Bootstrap: Expose bind() in ListGroup
Widget: Simplify binding to channels