calendar: add elm.swallow.background part to all of groups
calendar: add elm.swallow.background part to all of groups

Summary:
elm.swallow.background part will be a default part for
widget's background image.

Test Plan: N/A

Reviewers: woohyun, kimcinoo, cedric, Hermet

Subscribers: Hermet

Differential Revision: https://phab.enlightenment.org/D3676

Signed-off-by: Cedric BAIL <240633aa59d25638de9800ef43a88ad2e208d24d@osg.samsung.com>

tasn/elementary,tasn/elementary,tasn/elementary,tasn/elementary,tasn/elementary