[db] adds check to make sure rank is greater then 0
[db] fixes rosbee example - some connections were missing
[db] moves connection (source/sink) lists from being stored in
individual vertices and edges to master lists in topology - this makes
the values be dynamically querried and reduces the likelyhood of getting
corrupted information if one list gets decremented and the other does
not
[db] updates the dava.xml example