Fix so birthdays are exported with correct year and recurrence definition (T855)

Summary:
Refactored birthdays handling code. The "all birthdays" request is detected
and for this case year is not modified and recurrence rule is added.

Reviewers: #roundcube_kolab_plugins_developers, vanmeeuwen

Reviewed By: #roundcube_kolab_plugins_developers, vanmeeuwen

Differential Revision: https://git.kolab.org/D117