Improve flexibility and performance of pipeline REST API
Improve flexibility and performance of pipeline REST API

- desired output can be spectified in the URL call

- pipelines are stored in a 'least-recently-used'-cache to avoid
  repeated initializations of pipelines

- image output is encoded as PNG

- result dict is serialized using msgpack (instead of a JSON string)
  for better compression and performance when transmitting pictures

BioroboticsLab/deeppipeline,BioroboticsLab/bb_pipeline,BioroboticsLab/deeppipeline