MAJOR BUG FIX in getFirstSpaceFromSpec() of SpaceRepository.
This function never uses its parameter, and replies the first instance of space in the repository (even if not matching the given specification).
This function is refactored to get the SpaceID from the space specification, and returns the Space from this SpaceID.
Add getSpace() is AgentContext.
According to sarl/sarl#58, the function getSpace() was
added in AgentContext.
The Janus Context class is refactored to reflect this change.