frontendapp compatibility
- add support for separate not found page for 404s (not_found.html)
- support for exception handling with error template (error.html)
- support for home page (index.html)
- add memento headers for replay
- add referrer fallback check
- tests: port integration tests for front-end replay, cdx server
- not included: proxy mode, exact redirect mode, non-framed replay
- move unused tests to tests_disabled
- cli: add optional werkzeug profiler with --profile flag
