modules/http_client: less ambiguous error logging
move send_reply to ircconnection
modules/http_client: tighter Command integration

The Command class now has http_get and http_post added as wrappers to
the methods added to the Bot module. This allows us to include the
message object with the http request so that errors can be sent to the
user that triggered them.
modules/http_client: add optional silent_err parameter
scripts/lastfm: use new http_get