Upgrade Mercedes API usage for authentication & tokens retrieval (issue #34)

[samfaitmalomolet]

(FInally I found out how to create a PR from a fork 😄) Fixing issue #34

• Change URLs to new API for oauth2 as mentioned here (slider §2.2)
• Add openid to scope as mentioned here (slider §3.1)
• Fix small copy-paste issue in shell script