CCO: Availability Zones pricing

[ilya-kolchinsky]

As of now, the CCO displays (and internally uses) the same instance type price for all availability zones, while in reality there are minor pricing differences. It is important to take these differences into account when, for example, considering a tradeoff between reliability and cost.
Extend the CCO to fetch, present, and use for cost optimization the per-AZ prices.

[AdiY10]

Performed in PR #50
@ilya-kolchinsky please close the issue