Adding persistant Health and Repair ship function

Introduced new methods and a property, temp_hit_points, to ICharacterEntity, CPlayerCharacterEntity, and CNonPlayerCharacterEntity. These changes help us have a temporary storage for character set during a session, especially when the objects are re-initialized for reasons such as a scene reload. The 'get_temp_hit_points' method is implemented in CPlayerCharacterEntity but not CNonPlayerCharacterEntity as the latter does not need this feature. Some debugging lines have also been added temporarily to CInSpaceState to track this change.

Closes #4 (closed)