Skip XSL transformation for old Subsurface format

Making sure the XSL transformation does not occur on Subsurface's old
XML format. A deeper inspection on the XML content is required as
MacDive and Subsurface (old format) have the same root element (dives).

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Support for Imperial units on MacDive log import

The cylinder size is treated as metric as the samples received indicate
it would be so.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>