add rewriter_handler, frame wrapper support!
refactor:
- move is_identity(), is_embed() to wburl from wbrequest
- add is_mainpage() predicate
- add create_template() to each J2TemplateView to create itself
- add HeadInsertView to create a reusable head insert for
RewriteContent
- add 'mp_' as modifier for frames mode to be used as possible
  modifier with HTMLRewriter
ChunkDataReader: if determined to be non-chunked, read full buffer
unchunked
support both frames and non-frames mode
add automatic framing when in framed mode
live rewriter: integrate handler with rewrite_live.py module,
clean up css, add unit and integration tests
clean up cli server now known as 'live-rewrite-server', which performs live rewrite using
iframe paradigm