* Improve benchmark configurations:

* Move data downloading from configs to download_data.py. Add an alternative download link.

* Add Data class to operate data loading and indexing.

* Add Metric class to operate benchmark runs.

* Benchmark results are now the median or geometric mean of benchmark
  runs.

Benchmark framework impl; add YuNet for face detection, DB for text detection, CRNN for text recognition

* benchmark framework: benchmarks based on configs

* added impl and benchmark for YuNet (face detection)

* added impl and benchmark for DB (text detection)

* added impl and benchmark for CRNN (text recognition)

* add readme
* add license
* add git-lfs tracking for Caffe, Tensorflow, Torch, Darknet & ONNX model weights.