Improving Eurolite Mk2 Serial Number discovery/config

[peternewman]

I don't know what you think about this (maybe as a future enhancement for another PR):

1. Start up OLAd in enable_eurolite_mk2
2. If no (non-blank) eurolite_mk2_serial set (at startup), it adds each found one to the list
3. So workflow wise you could plug in your Eurolite dongles, turn on the setting, run up OLA. Turn off the setting and plug in your other devices.
4. Upsides you wouldn't have to read logs or find serial numbers via other methods
5. Downsides some potential confusion if you don't follow the right workflow
6. Alternative suggestion is do the same thing but put them in another key (e.g. discovered_eurolite_mk2_serial) which you could rename if required.

Originally posted by @peternewman in #1888 (review)

I was just trying to think through how someone will use it. If like you I've got one Eurolite Mk2 and one Enttec, I find I can't use them both together unless I enable the serial number mode, but how do I find the serial number? If what's printed on the bottom of the unit is exactly what I need to type in, then perfect, but otherwise I was thinking OLA could effectively pull either any serials it finds, or the serials it found in the last run, into the config file, for you to copy and paste. Otherwise you need to either use lsusb or trawl through all the OLA logs or similar. But you're the one using the kit, does that make sense as a workflow or seem redundant?

Originally posted by @peternewman in #1888 (comment)

Someone would now indeed have to look at the OLA output or lsusb to find the serial number -- this is indeed not super user friendly. What would be really useful is if this could be configured on the web interface (including that the interface would show the serial numbers), but that's a whole different scope ;). What's currently implemented at least demonstrates the use of the serial number to solve the conflict. In fact, given that quite some modules conflict with each other, a future idea could even be to incorporate this in a more generic way so that the user would be shown the possible serial ids and select the right device for it.

Originally posted by @aroffringa in #1888 (comment)

[aroffringa]

As an additional motivation to use serial checks more generically: I've been using the Eurolite 'serial' fix for a while, and while it is very nice that I can now use two otherwise conflicting usb interfaces at the same time, what I actually like even more about the fix is that I don't have to start disabling/enabling plugins if I switch from one interface to the other: with the same configuration I can just connect either interface (Eurolite or Enttec in my case) without configuration changes.