MainFX tweaks should be user-storable

[adcxyz]

Currently, there is no convenient way to save the current settings of MainFX
as a new (or modified) MainFX preset.
should modified preset go to userPool dir, and not to quark POOL dir?

storing should be nested settings :
MainFX should know which slotsToStore (and which not)
When storing, keep:
name of MainFX preset,
all active slotNames,
for each slot, param names and values
when switching:
add the active slotsToStore,
remove unused slotsToStore

[adcxyz]

Missing: ProxyChainPresetGui class

[adcxyz]

ProxyChainPresetGui class exists now