Add direction for FoldablePlugin

[kombatkos]

I would like to be able to choose the direction of the insert generators (before/after)

[NullIsOne]

Current implementation is not support it and even not every Table/Collection Manager have required functions to insert generators before some anchor generator.

Take a look at ManualTableManager.insert(before. This old method preparing indexes for new generators and using common BaseTableManager.insert(elements. You can take this as reference and add same insert(before for other Manager like BaseCollectionManager

When insert(before will be ready you can update current FoldablePugin or made a custom implementation.
With custom implementation you can even replace FoldableItem with new protocol to control insert direction before/after right in this new FoldableItem. Custom solution will be more universal, because you will have an ability to insert new generator in different directions inside one table or collection.