better default vdir storage path using $XDG_DATA_HOME

[Xavier Brochard]

IMHO the default config path to contacts and calendar vdir directories should be
~/.local/share/vdir/contacts and ~/.local/share/vdir/calendar

Of course user's can change that, but the config file should offer a modern storage path according to $XDG_DATA_HOME default.

[Hugo]

Why not ~/.local/share/calendars/ and ~/.local/share/contacts?

(coincidentally, this is actually what I'm currently using).

[Xavier Brochard]

Because one could already use these paths but not in vdir format.