Issue #5: encapsulated VideoSourceBlackmagicSDK into USE_BLACKMAGICSDK macro in video source factory
Issue #5: encapsulated VideoSourceBlackmagicSDK into USE_BLACKMAGICSDK macro in video source factory

gift-surg/GIFT-Grab,gift-surg/GIFT-Grab,gift-surg/GIFT-Grab,gift-surg/GIFT-Grab