Quality improvements (mozilla#29)

Update README.md

Minor improvements (mozilla#20)

- Flores dataset importer
- custom dataset importer
- ability to use a pre-trained backward model
- save experiment config on start
- stubs for dataset caching ( decided to sync implementation with workflow manager integration )
- use best bleu models instead of best ce-mean-words
- fix linting warnings

Bicleaner support + fixes (mozilla#13)

SacreBLEU is a regular importer now and evaluation is not limited to sacrebleu datasets.
fixes

Added bicleaner-ai and bicleaner filtering (one or another based on available pretrained language packs).
fixes


Added script to find all datasets based on language pair and importer type, ready to use in config
fixes


Fixed conda environment activation to be reproducible on GCP

Other minor reproducibility fixes

Add reference to bergamot project