DAVdroid: use "standard" flavour

DAVdroid now uses flavours, and "standard" is the default flavour.

Added 2170 commits:

• d7148a92...9ec2c8f8 - 2169 commits from branch fdroid:master
• e8a942d3 - Use "standard" flavor

mentioned in commit e4cdff01

Status changed to merged

Mentioned in commit niedzielski/fdroiddata@e4cdff01