DatasetService: provide SCIFIOConfig signatures

The save and load methods of the DatasetService now offer configuration
via SCIFIOConfig signatures.
Create OpenDataset command

Add a new command for opening datasets. This allows configuration input
harvesting.
Create SaveDataset command

Added a command for saving a dataset. Provides the option for
configuration input harvesting if desired.
DatasetIOPlugin: use save/open dataset commands

Refactored to use the Save/Open Dataset commands. This will trigger
additional configuration options to be harvested, facilitating a more
flexible I/O experience.
Merge branch 'create-dataset-commands'

Adds commands for opening and saving datasets. Using commands gives us greater
flexibility in configuration, and we can now expose options such as cropping,
image ranges, and file grouping.