Add a patch prelude for formula modulators

[blancoberg]

Is your feature request related to a problem? Please describe! All custom functions, tables, and variables in the formula modulator have to be declared in the init() function of each note, even though it would be much more convenient if they were already declared upon preset load.

Describe the solution you'd like: Create a "patch prelude." It's similar to the prelude section, but it is editable and saved within the preset. Everything declared in that section should be accessible globally by all formula modulators, just like the regular prelude.

This would make it much more efficient to create custom classes and handle large tables without risking lag on each note.