Warn about hazzards when test Power > 0

[easytarget]

Default Test power is set to 0 for a reason (it has safety ramifications, so we force users to explicitly enable it). This is not, however, very well described.

When the user changes this value away from zero we should use a popup + confirm to warn about the safety hazards.

If test duration is 0, aka no limit, we should reinforce this with a info/warning box in the settings panel when duration = 0 and power is > 0.

Finally, if test power is zero, we should hide (or shade) the 'test' button in the control panel since it is inactive.