Add FIL CLR button

[Tyrbiter]

I think it would be nice to have the ability to clear modifications made to the base filter settings via the FIL CLR button, perhaps have this at the right edge in line with the existing FIL A, B, C buttons.

[tonyc]

Noted - this will require reading the defaults for A, B and C, and storing them somewhere. Unfortunately there is no FIL CLR command to simply reset the current filter.

[Tyrbiter]

Interesting, given that there is button on the front panel I had hoped it would be straightforward.

Oh, yes, just looked at the SL and SH commands. A bit of a mess to be honest.