Fitting Window: Create a Drop Down ROI Menu Widget

[JackEAllen]

The redesign of the Spectrum Viewer Window will likely involve a few different iterations as this area of Mantid Imaging is actively being developed until the point where a Bragg edge offering have matured as a feature.
Due to this volatility to the GUI, we should place components into Widgets where possible and sensible to do so to make it easy to re-use where applicable throughout other sections of the Spectrum Viewer in the future if needed and also allow for easier relocation of existing components.

Create a ROI selection widget which allows the user to select one ROI from the ROIs created by the user within the Image window

Drop Down Menu:

Fitting Window: