Rename SR_CONF_OUTPUT_* to SR_CONF_*.

Rename SR_CONF_OUTPUT_* to SR_CONF_*.

All those options are currently applied only to power-supplies
but they could apply as well to electronic loads, except for the
fact that electronic loads channels are called inputs and not
outputs.
Also when you think about an SMU (or any kind of 4-quadrants
power-supply), their channels can both source and sink current,
so they can be considered as input as much as output.
Those SR_CONF_* are thus renamed so that they can be used in all
those situations.