Implementation of *wampcra*-based client authentication for crossbar router. ([auth based on challenge-response mechanism](https://crossbar.io/docs/Challenge-Response-Authentication/))

PR also adds additional `datadir` parameter to `golemcli`.
You can view, comment on, or merge this pull request online at:

https://github.com/golemfactory/golem/pull/3171

— Commit Summary —

* Merge
* Working ticket auth
* Working ticket verification
* Adding tests
* Cleaning
* Cleaning

— File Changes —

M .gitignore (1)
M golem/interface/websockets.py (11)
M golem/node.py (16)
M golem/rpc/cert.py (35)
M golem/rpc/router.py (78)
M golem/rpc/session.py (20)
M golemcli.py (25)
M tests/golem/interface/test_golemcli.py (1)
M tests/golem/interface/test_websocket_cli.py (6)
M tests/golem/rpc/test_cert.py (19)
M tests/golem/rpc/test_router.py (30)

— Patch Links —

https://github.com/golemfactory/golem/pull/3171.patch
https://github.com/golemfactory/golem/pull/3171.diff