Possibility to handle long text

[MagMar94]

Closes https://github.com/CFenner/MMM-Sonos/issues/30

Makes it possible to truncate long text, or make it scroll in the allocated space.

The scrolling is based on this scrolling text generator. It is difficult to find the exact width of the text, but I found that multiplying the text length with 1,1 gives decent results. Some text will probably be longer, especially strings with lots og ms and wide characters. The current unit is ch, which is defined as the width of the character 0 (zero, or U+0030) of the font.