[teamup-rocketchat] improve error reporting

[individual-it]

This should be done in multiple PRs

• when starting the bot with invalid configuration it just silently fails not telling the user what went wrong
• giving wrong Rocket.Chat details just logs Unauthorized in the log file. This is not enough to debug the issue

[individual-it]

• when full day time entries are read we get the message Error while converting time stamps, what is missleading