Fix automatic retries when authentication fails

[prempador]

Motivation: Issue #10

• We know for a fact, that failed Authentication will cause to many follow-up requests
• We think that the random behavior mentioned in the Issue are caused by expired refresh_tokens the missing space character in the Authenticator class

This PR:

• Adds logic to the tokenManager, that causes it to retry authentication with API-Key and API-Secret if the authentication with the refresh_token fails
• Adds logic to the Authenticator, that causes him to give up, if the last request that came back with a 401 error already had an authorization key
• With 5724599 also adds a Test-Class to prove the changes work as expected

Possible Problems:

• Authenticator might return null too soon if resfresh_token is expired, need someone to check if this is true This was the case. Changed in f5db52b