Fix dsp/gui inconsistencies and improve generic UI

[falkTX]

Changes should be self-explanatory, but to summarize:

• DSP and UI should start with the same state, otherwise UI will show incorrect values
• Enumerations are nice so hosts that use generic UI can show those as the real parameter values instead of just numbers
• The gain controls were set as logarithmic, but no log scale was ever in use in the GUI, removed the hint to make DSP side behave the same as the UI does

[pdesaulniers]

LGTM! However, do you know if these changes could introduce backward compatibility issues in some hosts? For instance, could automation behave differently if we change the scale of the gain parameters from logarithmic to linear?

[falkTX]

For instance, could automation behave differently if we change the scale of the gain parameters from logarithmic to linear?

On LV2 where the host reads those flags, it uses real values so it will keep being the same.
On VST2/3, maybe.. but this was always wrong anyhow since you cant have log scale with a 0 target (min or max)

[pdesaulniers]

Good, I'm merging this. Thanks!