taskboard workflow and project DnD

platform: 2.0.4, 2.1.5, 2.2.0 # supported: 2.0.4, 2.1.6, 2.2.1
backlogs: master # supported: 0.9.33
ruby: 1.9.3, 1.8.7 # supported: 1.9.3, 1.8.7

fixes #735
fixes #785