Fix for basic auth with @ in username

[hardillb]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Manually build the Authentication header to work round URL encoding problem

Also add support for user/password in URL e.g.

http://user:pass@www.example.com

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage decreased (-0.01%) to 67.525% when pulling 919aee6 on hardillb:dev into 4acb66f on node-red:dev.