ecore: Added getting "WarningLevel" on upower module.

ecore: Added getting "WarningLevel" on upower module.

Summary:
From UPower 0.99.0, a property "OnLowBattery" was removed and
upower have recommended to use "WarningLevel" instead.
This revision provides "WarningLevel" using the property "DaemonVersion"
and it keeps dealing with "OnLowBattery" as well for old system.

Fixes T1909

Reviewers: gwanglim, barbieri, zmike, stefan_schmidt

Reviewed By: barbieri

Subscribers: zmike, stefan_schmidt, cedric

Differential Revision: https://phab.enlightenment.org/D1717