REACH-115 Separate SaveUploader into Model layer and View layer

`BaseSaveUploader` is base class for `NWKSaveUploader` one. `BaseSaveUploaderView` isn't base for `NWKSaveUploaderView`.
Ah, perhaps this is why you put the `SaveUploader` model in `App` rather than `DynamoApp`.  It looks like you're not guaranteed to have it.  You can ignore the above comment for now, but I've created a separate task to create `DynamoAppView` with corresponding UI components.