fixes #2317 fixes #2318 fixes #2319. Various issues with edge bends are fixed by creating a clearer distinction between defaults, mappings, and bypass values in the code.
Merge branch 'develop' of github.com:cytoscape/cytoscape-impl into develop
Refs” #2320: “Visual Style" replaced by just "Style” on the UI.
Refs #2327: Continuous Mapping for “Node Size” always works now
This reworks the View menu a little to separate out the "Open Custom
Graphics Manager" menu.  Fixes #2329

Change-Id: I330dbfb12525be9e31db0866d5000650cbe4469e