Break custom messages by newline

[seriyps]

Right now /run/pixelpilot.msg is only read once per-second and if there are multiple messages written to it during this second - they will be glued together (and currently \n us displayed as empry unicode square by, eg, popup widget).

Let's make sure to:

1. Emit separate fact that is terminated by \n
2. If buffer doesn't contain \n then keep reading and buffering untill there is \n or buffer size is exceeded
3. If user wants a newline to be part of the message fact, then a newline should be escaped \\n; the parsing code should make sure to unescape it
4. Make sure popup widget can display messages containing newlines by actually adding a new line