Fix addSingleItemCollectionBuilders when useImmutableCollections is false

[Randgalt]

• Removed SingleItemsMetaDataMode.STANDARD as it wasn't used
• Removed needs*MutableMaker - always add them when corresponding needs*Shim is true
• Merged addMutableMakers() into addShims()
• Always use mutable makers when addSingleItemCollectionBuilders is true

Fixes #129

cc @mads-b, @freelon, @tmichel

[freelon]

• needs*Shim is now used for shim and mutable makers. It should be renamed to reflect its meaning.
• if only addSingleItemCollectionBuildersis true (i.e. lists are mutable) the setters for collections always create an immutable copy of the collection passed to it
  • if an item is added to that list another copy is made to make it mutable again
  • not sure what's the way to go here, but I'd prefer to be still able to set a fixed list instance (see this discussion for a more explicit way of creating a new list with all items of a collection (clear and addAll))

[freelon]

On a separate note, now if I use the collection setter (addSingleItemCollectionBuilders=true) with e.g. an ArrayList I'll get an exception later if I try myRecords.someList().add(...) because it became immutable without me asking for immutable lists..

[Randgalt]

I see - these two features may be hopelessly broken: addSingleItemCollectionBuilders is the real troublesome one. I'll think more about this and possibly do something similar to this