[db] makes sources and sinks for bands generated rather then static
lists
[db] renames Band sources and sinks to emitters and collectors
(consistant with the terminology used with snaps)
[db] adds asciidraw - a more objectifed start to asciiplot
[db] adds "visual" attributes and isSource/isSink methods to Snaps
[db] changes isSource/isSink from properties to methods
[db] adds xml test files
[db] adds unittests
[db] Band Emitter/Collector only report snaps that touch that band
[db] updates comments in unittests