Added wells to groups.
Added new WellSet class - just a thin wrapper around std::map
Implemted Group with external WellSet class.
Added groupName as a DyanmicState<std::string> property of the Well class
Added createStep flag to Well constructor to be able to track well creation time.
Added createTimeStep to Group constructor to keep track of group creation time
Will create and delete Group <-> Well relationships based on the WELSPECS keyword.
Changed createTimeStep -> creationTimeStep for readability.
Merge pull request #56 from joakim-hove/group-has-well

Added wells to groups.