Created method addDNANode() to add only a DNA node 
to a pre-existing mRNA node. Combine this with 
method addCentralDogmaNodes?
Finished mRNA section - if prefix protein is 
present, then need to remove repetive "prefix_mRNA" 
factor. if prefix protein not present, then only add DNA node.
comment outline for "_" modifications added
Added logging statements for degbugging.
Uncommented class