ouroboros-cli backproject fails due to invalid slice-options

[den-sq]

When using the CLI, backprojection fails because the pipeline expects both the backprojection options and and the slice options as objects, but the CLI only passes the backprojection options (and thus the verbose flag gets passed as the slice options).

Simple fix to load slice options from the file specified in the backprojection options, works when applied locally, will have a pull request up in a minute.

[den-sq]

Fixed by #2