v0.7.1: updated REST API; fix bfloat16 issue; dockers w/ both arm64, amd64

• Bfloat16 is not default and used only when it is available
• /translate REST API is updated
  • accepts params lp_alpha, beam_size, num_hyp
  • produces n-best hyps, scores, time taken per API call
• Web APP: relative paths to static files are correctly updated when base prefix is used
• Docker files are updated. multi-arch build with linux/arm64 linux/amd64 have been released to docker hub