Add irc to test_parse_privmsg_nick method name.
Make privmsg command parsing case insensitive.

Partial fix for #71.
Add channel to stubbed irc_message_parse result.
Fix parse_irc_privmsg unknown from nick.

Return an empty string when the from nick is unknown.
Fix test case class names.
Move message_out_cb tests to test_message_out_cb.py.