This fix is mainly so I can mass-add series _and_ movie entries using a
`IMultiItemResolver` without having to resort to complicated logic
using _both_ a `IItemResolver` and a `IMultiItemResolver` by splitting
up what gets added where.
I've also added three new interface methods to the `IDirectoryService`,
one of which is used in the modified
`ResolverHelper.SetInitialItemValues(…)` to get the file system entry
info for the item regardless of which type the file system entry is.
In my local testing so far I haven't found any issues introduced
by this change.
Mikal Stordal