Crossbar

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* new: bump dependencies
* new: CI use newer ubuntu and newer pypy
* fix: copy license file to root folder (1825)
* fix: check for io_counters feature - macos (1826)
* new: proxy improvements (maintain and RR multiple backend connections)
* new: function-based custom authenticators (for more authmethods)
* fix: proxy/rlink management API

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* fix: "crossbar stop" subcommand crashes on Windows (1802)
* new: use core20 for snap runtime (1798)
* new: include node authid in generated node key file
* new: web+router+proxy worker mgmt api polish + docs
* new: refactor/cleanup IRealmContainer
* fix: management API of proxy workers
* fix: improve and polish log output of nodes

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* new: various fixes and improvements to rlinks
* new: proxy worker management API
* fix: turn down log noise

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* fix: management procedure "get_router_realm_links" return value not serializable (1781)
* fix: we always have publisher/caller information (1778)
* fix: attribute name (removed underscore)
* fix: webservice of type "path"

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* new: bump CI to py 3.8
* fix: rlink fixups (1777)
* fix: node shutdown option processing
* new: Configurable cookie headers issue-1511 (1753)
* fix: fix backend closing behavior for proxy worker (1754)
* new: proxy class authenticator 2 (1764)
* new: add mgmt api to lookup realms by name in router workers
* fix: varies proxy worker fixes and cleanups
* fix: backend closing behavior for proxy worker

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* new: proxy worker backends support wamp-cryptosign backend authentication using node key
* new: proxy workers fully support all authentication methods for frontend session
* fix: rectify proxy worker glitches and refactor proxy worker code