Squish Tests: Spectra plot mode

As a developer I would like to verify the following behaviour using Squish:

- In the `DAE` perspective, in the `Spectra Plots` tab, change the mode of one of the plots.
- Verify that the change is reflected on the graph.

#### Additional info:
- We can use the `title` property of the `Axis` object to verify the change.
- This test may be brittle as the spectra plots are implemented via an OPI, so any change to the OPI is likely to need a corresponding test change. Consider implementing other (easier) squish tests first.