#74 metadata branch creation

[Nick Juty]

Issues highlighted here:
http://sbml.org/Forums/index.php?t=tree&goto=6554&rid=0
A subsequent survey found there to be a need to a metadata branch. Results are here:
http://sbml.org/Forums/index.php?t=tree&goto=6698&rid=0

Initial metadata branch terms created will use this tracker number. Other community suggested terms should submitted as regular tracker items.