assign capabilities to ecal->capabilities so that it need not be computed

assign capabilities to ecal->capabilities so that it need not be computed

* libecal/e-cal.c: (load_static_capabilities): assign capabilities
to ecal->capabilities so that it need not be computed repeatedly.
* backends/groupwise/e-cal-backend-groupwise.c:
(populate_cache) : added message to view element to recieve
message bodies as plain text (default).
(connect_to_server) : the Tasks folder is also Calendar and
not Checklist in GW server.
(e_cal_backend_groupwise_get_static_capabilities) :
Added CAL_STATIC_CAPABILITY_SAVE_SCHEDULES.