Improve implementation of SNR Task

[laurencejackson]

SNR task requires additional features:

• the task takes 2 input series, which requires the functionality to select multiple series in the workbench
• the SNR task takes an additional variable measured_slice_width which is the output for the slice_width task. Users could enter this manually, eventually we can add a feature to suggest a value if that task has already been performed.

[sophie22]

Are images for SNR measurement always going to be separate Series or is it just how it is in the test dataset? I added a text input field to get the slice_width variable and pass it to the task running the SNR script.

[tomaroberts]

The SNR task is currently working, but the implementation needs improving. Currently, you have to select two SNR images, then process. The final report is associated with one of these two images, but the other image sits dead in the Workbench table.

For example, when uploaded, the files look like this in Workbench:

When running the SNR Task, the user must select both Series, which is currently quite unintuitive as the majority of other tasks require selecting one series:

Once the SNR Task is run, the Workbench looks like this:

Again, this could be better because currently it's not obvious to the user that the report applies to both of these Series.