Calculation preconditions

[mkurek]

There should be extra step before calculating costs: checking plugins and overall preconditions. If plugin raise precondition error, calculation for single day should be interrupted.

Possible plugins preconditions:

• cost is defined for every warehouse/data center
• team cost is defined
• dynamic extra cost is defined
• price is defined for every usage type in pricing service with fixed prices

Posible overall preconditions:

• check if there is any cycle between pricing services
• check if costs for single day (and type - forecast and real) was already accepted

Notice that preconditions could be checked for single day or for interval.