Take the keyring init from the client-api-server and the monolith out to a
shared file

This seems to have been missed when we folded all the readers and
writers packages into routing.

* vendor: Add bimg image processing library

bimg is MIT licensed. It depends on the C library libvips which is LGPL
v2.1+ licensed. libvips must be installed separately.

* mediaapi: Add YAML config file support

* mediaapi: Add thumbnail support

* mediaapi: Add missing thumbnail files

* travis: Add ppa and install libvips-dev

* travis: Another ppa and install libvips-dev attempt

* travis: Add sudo: required for sudo apt* usage

* mediaapi/thumbnailer: Make comparison code more readable

* mediaapi: Simplify logging of thumbnail properties

* mediaapi/thumbnailer: Rename metrics to fitness

Metrics is used in the context of monitoring with Prometheus so renaming
to avoid confusion.

* mediaapi/thumbnailer: Use math.Inf() for max aspect and size

* mediaapi/thumbnailer: Limit number of parallel generators

Fall back to selecting from already-/pre-generated thumbnails or serving
the original.

* mediaapi/thumbnailer: Split bimg code into separate file

* vendor: Add github.com/nfnt/resize pure go image scaler

* mediaapi/thumbnailer: Add nfnt/resize thumbnailer

* travis: Don't install libvips-dev via ppa

* mediaapi: Add notes to README about resizers

* mediaapi: Elaborate on scaling libs in README