Add APIs to manage logistic groups

[Sharparam]

There doesn't seem to be any APIs to manipulate logistic groups for mods. This makes it impossible to implement custom combinator UIs where the user needs to be able to select and manage logistic groups, just like with base game combinators.

We need APIs to:

• Get all existing logistic groups (with the count of how many things are using the group)
• Create logistic groups (maybe not necessary as an API as just setting the "group" property on a section will implicitly create it)
• Delete a logistic group

Context:


This is the base game "Change logistic group" dialog which shows the existing groups and allows the player to select or delete them.