Fix authorization issues with mock resources

[jonathan-r-thorpe]

After doing some controller testing of nmos-js using authorization the following issues were identified:

• The Auth server causes cross origin errors in browsers when using authorization code flow authentication
• The mock Auth required the use of private key JWT - however, this is optional
• The mock Auth required scopes to be supplied on token refresh - however, this is optional
• The mock Node was not authenticating its API
• Both mock Registry and Node had poor responsiveness when using authentication mainly due to the token evaluation process being expensive

The following fixes were introduced:

• Wrap the mock Auth server in a CORS wrapper
• Make use of private key JWT optional
• Cache scopes on authentication to use on token refresh if scopes not supplied.
• Factor the authentication checking into a utility function
• Add authentication to the mock Node
• Introduce auth caching on Registry and Node so decoding of tokens only happens once for each scope

[jonathan-r-thorpe]

Checked for regressions against nmos-cpp on Windows/Ubuntu with authorization enabled/disabled.

[lo-simon]

Just a couple of minor suggestions, rest LGTM.

[cristian-recoseanu]

Seems reasonable, however, I do not have an environment where I can test this change.