Merge pull request #479 from demaagdk/develop

remove vpx from class context
Merge pull request #480 from demaagdk/develop

remove class-level vpx
more vpx fixes
Merge branch 'develop' of github.com:sightmachine/SimpleSeer into develop
Fix motion plugin when db empty
Frames only publish on frame/ channel if the frame is new (so backfills don't create unnecessary realtime traffic)