Correct issue where messages were over-trimmed

Correct issue where messages were over-trimmed

In an attempt to correct a problem with quasseldroid multiline
messages (97a9b1646bb0d6362cef14bac3a577481cc01e49) the core started
trimming leading whitespace from lines. This broke pasting of things
like formatted code.

This commit ensures that only the splitting is done, and that we skip
empty lines when handling /SAY since they sometimes cause issues on
networks and the clients which split client-side already skip empty
lines.

Closes GH-331.