Add a new type to distinguish between closed circuit (CCR) and semi-closed circuit (SCR) diving. Some dive computers from HW and DiveSystem/Ratio support this. Because the CCR/SCR abbreviations are more commonly used, let's take the opportunity to also rename the existing DC_DIVEMODE_CC. To preserve backwards compatibility, a macro is added to map the old name to the new one. Reported-by: Jan Mulder <jlmulder@xs4all.nl>