Set user when logging time

[bufke]

Right now time is logged by the user account who has access to Redmine. It notes in the comment who the actual user is. It would be better to just post as that user.

It should be possible with the User Impersonation feature with Redmine's api. We could match the user based on the existing code to do that and have it try to post as that user if permissions allow.

Hopefully I can submit a pull request for this soon.