Merge pull request #153 from laarmen/irc_notify

ircbot: Use notices instead of actual messages
Core: fix a typo in warning category

DeprecationWarning instead of warnings.DeprecationWarning
DeprecationWarning is a built-in exception class
Core: add unit test case for FedMsgContext.send_message

it tests that send_message()
- deprecation warning is properly displayed
- it calls publish() with correct arguments