MarketContractOraclize: Use absolute timestamp to Oraclize query, move time checks to constructor, introduce const variable, lower callback cost.
MarketContractOraclize: Use absolute timestamp to Oraclize query, move time checks to constructor, introduce const variable, lower callback cost.

Apply changes after PR #59 findings:

* use absolute timestamp to oraclize_query
* move time checks to constructor
* introduce a constant variable SECONDS_PER_SIXTY_DAYS
* lower Oraclize callback cost to 150000.

Issue: #57

MarketProject/MarketProtocol,MarketProject/MarketProtocol