rename some system page tabs, in an attempt to make things clearer

    Commands -> Power
    Power -> Power Settings
    Scheduler -> Scheduler Settings

It was not obvious from the name "Commands" that this means power
control. The "Power" tab under "Configuration" was also too tempting
a target when looking for power controls. This attempts to make things
a bit more obvious.

Change-Id: If591e2101b01a89d5d127b82b79ca6d3896ce98f