Attachment support for Groupwise calendar and task items.

Attachment support for Groupwise calendar and task items.

* backends/groupwise/e-cal-backend-groupwise-utils.c:
(e_cal_backend_groupwise_set_attachments_from_comp),
(set_properties_from_cal_component), (get_attach_data_from_server),
(set_attachments_to_cal_component), (e_gw_item_to_cal_component):
Attachment support for Groupwise calendar and task items.
(e_cal_backend_groupwise_store_settings): Remove unused variable.
* backends/groupwise/e-cal-backend-groupwise.[ch]:
* (populate_cache), (e_cal_backend_groupwise_finalize), (e_cal_backend_groupwise_open),
(e_cal_backend_groupwise_notify_error_code),
(e_cal_backend_groupwise_get_local_attachments_store):
set the path to the attachment store in the filesystem.
* libecal/e-cal.[ch]
* (e_cal_init), * (e_cal_finalize), (set_local_attachment_store), (e_cal_new),
(e_cal_get_local_attachment_store): Add a new member to ECal that
stores the local attachment store for various backends.