Break out into separate assembly

[intvsteve]

Make compressed archive access be discovered via MEF so it's more completely isolated.

[intvsteve]

Unlikely that we're going to do this:

• Use of PathUtils (INTV.Shared)
• Use of TemporaryDirectory (INTV.Shared)
• Use of PathComparer (INTV.Shared)

So, while it's possible it could be made, it's likely one or more of the following would also need more work:

• IRomHelpers(barely aware ofICompressedArchiveAccess`)
• StorageLocationExtensions makes significant use of it

There may be a few other types that have leaked out to the wider code as well.

Possibly the IStorageAccess interface and StorageLocation type could be extended to make this more completely transparent. However, the notion of needing to know about archive is still necessary when we consider backup / restore features - meaning that the interfaces would either need to be defined in INTV.Core or INTV.Shared anyway, and we'd face possibly more MEF fun`.