* fix gpu CMD and set tag to latest
* udpate dockerfiles. resolve race condition of index creation with multiple workers
* update dockerfiles for preload. remove try catch for elastic index creation
* add back try/catch. disable multiproc in default config to comply with --preload of gunicorn
* change to pip3 for GPU dockerfile
* remove --preload for gpu
* remove env variables from dockerfiles
* add more config options to rest api. make fields optional. change to elasticsearch as default
* skip reader if retriever doesn't return anything
* add more config params to farm reader. fix top_k_per_sample
* update FARM version
