Implement broadcast events for extra switch on Tekla SEP

Specification http://wiki.scyp.atrc.utoronto.ca/w/Switch_Event_Provider#Switch_Event_Flow states no switch events are broadcast for the extra switch (on single 3.5mm jack plug), indeed they are not, but this would provide a much easier hardware connection for single-switch users. Propose updating specification with an appropriate value for "Android Switch Event Extra" and implement accordingly, please? :)