Android allows only having one address book per account, so until now
users of EteSync were only able to have one address book. This was
always an annoying limitation, but even more so now that journal sharing
is implemented.
Luckily, DAVdroid recently implemented multiple account support by
creating sub-accounts for address books.
This patch is an import of the DAVdroid changes, with adjustments to
work with EteSync, and a few changes that did not make sense for
EteSync. The original commits' split didn't provide any value over this
squash, and the amount of adjustments and addition needed to be done to
apply them, made me decide to squash this change together.
This commit is mostly based on:
dfec72ce6b8ff5e0780e9ac4418c81d080f4b60b
9817594da14ad8dffae18de386e14aeaf41312b9
