Provide an emulation subcommand for testing configurations

[dpb587-pivotal]

To make it easier to test some of the more complex conditional or edge cases without needing to run the bot.

$ delegatebot handle-message --config team.yml --time "2019-05-24T19:20:21Z"
Sorry, the team is offline right now (we work from San Francisco). Try pinging us again during work hours.