support retina and non-retina screenshots
support retina and non-retina screenshots

Give screenshots on retina displays an @2x in their filenames right after the device name so that the screenshots won't conflict when making a batch run with retina and non-retina devices.

kivlara/KSScreenshotManager,vovkasm/KSScreenshotManager,vovkasm/KSScreenshotManager,duk42111/KSScreenshotManager,duk42111/KSScreenshotManager,ksuther/KSScreenshotManager,kivlara/KSScreenshotManager,ksuther/KSScreenshotManager