Make FedEnableMask syntax more user-friendly

[elaird]

The current notation, e.g.
<FedEnableMask>934&amp;3%935&amp;3%936&amp;3%2079&amp;0%</FedEnableMask>
seems obscure to me.

What would you guys think of using something more readable, e.g. comma separated lists along these lines:
<EnableFeds>934,935,936</EnableFeds>
<DisableFeds>2079</DisableFeds>
and then having the FM build the correctly formatted FedEnableMask from them?

[sethcooper]

The enable mask notation takes into account the requested state of TTS and S-link for the FED. Technically there isn't a way to reconstruct that from a simple enable/disable flag, because we lack that finer-grained information. We'd have to make some assumptions on what the TTS and S-link statuses should be for those FEDs which are enabled/disabled in this way. I suppose enabled would imply that both TTS and S-link are on, but this detail would be hidden from the user. If we can make this clear in the naming of the parameter, or some other way, then I suppose it's ok.
We are not often editing this, though, and at this point I think we only use this for testing global run configurations in local, although we could at some point use it to activate the masking on configure feature (if preferred over masking on init for some reason).

[jhakala]

This seems to go hand-in-hand with the update suggested in #170.