GUI SETTING: Seed Randomness

[AlexMitchellMus]

In some situations, a user may need to reproduce the randomness of sfizz.

This is useful- if for example pitch_random is used in a sfz script- and the rendering of the audio track needs to be similar each time.

I propose a setting for Seed preference in sfizz. This seed would be used as a basis for all random opcodes in SFZ. With each different opcode generating a new seed off the base seed via multiplication or addition etc by a fixed amount. Each opcode would then be itself random, but reproducible.

For multiple identical opcodes in the same SFZ script- a counter would also contribute to the seed:

pitch_random seed = base seed x opcode seed x opcode index

Three settings for randomness:
auto (on/off button) = sfizz assigns new seed on each launch (default behaviour)
seed (text box) = show current set seed number- and allow typing in seed number
new (toggle button) = sfizz picks new random seed