[Feature Request] Add Period and Trainning duration info to the list-model-versions command

[toni-moreno]

Related to this comment https://github.com/regel/loudml/issues/375#issuecomment-669721615

> list-model-versions swarm@cpu@mean@usage_active@host_worker2_cpu_cpu-total@time@1m
version  active   loss     trained  
00       0.       116.357  1.       <---this one 7 days
01       0.       116.357  1.       <---this one 7 days
02       1.       63.588   1.       <--- this one only 1 day

I've notice that trained version doesn't save the trained period and how long the period trained was, and how much it has taken to finish the trainning, this information could help users to improve future trainnings

something like this...

> list-model-versions swarm@cpu@mean@usage_active@host_worker2_cpu_cpu-total@time@1m
version  active   loss     trained    "Trainning Period Duration"  "Trainning Period"      "Trainning process duration" 
00       0.       116.357  1.                7d                    2020-07-25/2020-08-01              15m34s
01       0.       116.357  1.                7d                    2020-07-30/2020-08-01              15m34s
02       1.       63.588   1.                7d                    2020-08-05/2020-08-06              5m34s

Thank you very much