Previous time index access for simulation functions and observers

* Added OPENFLUID_GetPreviousRunTimeIndex() primitive
* Adapted simulation engine to provide previous run information
  to wares
* Updated tests for time primitives
* Cleaned time and durations types definitions

(closes #71)
Merge branch 'develop' into devel-market
Fix AvailPacksWidgets variable in MarketClientAssistant

* Stored MarketPackWidget in map indexed by type package