Add some new battery sensors : energy_now, energy_full and power_now.

Summary:
Depending on hardware, Linux kernel exports battery state in
different files. Previously only charge_now, charge_full and current_now
were available in ksysguard. With this commit all are selectable.

While we have now screens with more than 1000 pixels height,
a percentage with 100 steps will show a ladder. This commit also
make the created graphs nicer by giving 1000 steps.

Reviewers: #plasma, davidedmundson, ahiemstra

Reviewed By: ahiemstra

Subscribers: anthonyfieroni, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28127