Sync tasks/todo with CalDAV using the SyncEvolution backend

[Vincent]

SyncEvolution seems to provide backend allowing to sync the fields of this app over CaldDAV, according to this bug https://bugs.launchpad.net/ubuntu/+source/syncevolution/+bug/1440294#yui_3_10_3_1_1436779283067_316 (click the "[...]" link to see the command lines).

CalDAV tasks support features implemented in this app, so it would be *great* to use SyncEvolution database. ownCloud, Cozy Cloud and Thunderbird Lightning already support synced tasks.

I wonder if it's possible to move the default storage into SyncEvolution database, as for the Addressbook and the Calendar apps (if I'm right on this point).