Plugin preset functions should return preset category paths not only names

[Andzelmas]

Rewrite the functions that return the preset names for the plugins (lv2 and CLAP).
Not only names but also a category path should be returned.
App_intrf should then create container contexts for each directory in the category path.
This is necessary for example for Surge plugin, since there can be many presets. They should be categorized.

[Andzelmas]

CLAP portion of this works, need to transition lv2 preset function to the same system