various fix for battery plasmoid

Fix access undefined value warning, when calling function in
logic.js, pmSource.data can still be null since it might not connect at
that time.
When brightness is passively changed from outer environment, don't
trigger the dataSource service call with a bool protector called
disableBrightnessUpdate.
Move more code to DataModel.onDataChanged, under the same idea with:
https://git.reviewboard.kde.org/r/108280/ , hence the plasmoid.status
will always be the correct value, the changing of plasmoid.status cause
tray make popup unfocus.
Remove ugly hack of resetBatteryData in logic.js.
Fix some anchor related warning in PopupDialog.qml

FIXED-IN: 4.10


REVIEW: 108355