adds a config parameter to disable ffmpeg, defaults to false
initial cut at collection model changes
fixing obv bugs in collection model; switches to habtm for collection membership; pulls membership assertions out of descMetadata (not yet tested, squash this commit later ;))
collection specs fleshed out and passing
pointing at latest release of hydra-head as a dependency, and upping rails to 3.2.11, which has a few critical security fixes