use ThumbSniper backend release v0.9.15

Update Dockerfile

use git release v0.9.14

Set Mongo connection timeout to -1

update to openSUSE Leap 42.3

use ThumbSniper backend release v0.9.12

use v0.9.11 in Dockerfile

use v0.9.10 in Dockerfile

use v0.9.9 in Dockerfile

added queue size stats for phantom queue

delete thumbnails oder than 6 months

use backend-v0.9.6 in Dockerfile