Move Defaults to carnival-core

[augustearth]

Defaults, which is a de-facto configuration object, currently lives in carnival-util. It is used there only by MappedDataTable to get the cache directory so vines can write cache data. As part of #59, we want to move away from Defaults to explicit configuration objects. One step will be to elevate/isolate Defaults to carnival-core so it can be more easily transformed into a configuration object.

Looking at the code, it seems we are already mostly there. Defaults is used by MappedDataTable writeToFile, an implementation of the the method in MappedDataInterface. MappedDataInterface is legacy code.... we should be able to remove it. The new Vine functionality should not rely on it.

Steps

• Remove MappedDataInterface
• Remove implementation of MappedDataInterface in MappedDataTable
• Move Defaults from carnival-util to carnival-core