Add explicit "excitation" modifier to tpchn file and other testpoint metadata.
Workstations need to know which channels are excitation.
Currently, this is done by the restricting excitations to certain channel number ranges: 0-10k, 20k-30k. This is needlessly restricting, and an overload of the channel number that makes code changes difficult.
Instead, lets add an explicit "excitation" option to the channels, and not limit the channel numbers.