GUI: Subframe refiner

Resolves #134 (closed), #132 (closed), #109 (closed), #76 (closed),

Added a new subframe to the GUI, Refiner, which inserts unit cell and instrument state refinement into the correct place in the workflow. This is not feature-complete, and the layout needs some work, but it's useful to have in the main branch to complete the GUI workflow.

There are a few underlying issues that need to be fixed, and I am working on those; these include

1. the ability to assign the space group, which should fix the merged statistics.
2. The functionality of the plot in this widget, which currently does nothing
3. Instrument state refinement.