correct setting metadata on CyNetwork; fixes #541

solution was to not filter out null metadata since it affects
cardinality when transposing with cytoscape object lists

added SetMetadataTest to cover setting metadata on network, nodes, and
edges

added mockito/objenesis as test dependencies to core module

extended test classpath to include all framework libs
do not set metadata for empty cy objects

fixes #569
add model revisions column if necessary

fixes #570
Merge branch 'master' into experimental