Improve sliceviewer lineplot functionality

[gemmaguest]

As part of the work for the ISIS Reflectometry interface's preview tab, users would like some additional functionality when displaying line plots on the embedded sliceviewer:

• allow the plot to be opened in an external window (so they have a fully functional plot they can interact with more easily)
• add functionality to find a peak on the plot and return the spectrum number

We should check whether this would be useful functionality to add to sliceviewer itself, or whether it should be added just to the reflectometry interface.

[stale[bot]]

This issue has been automatically marked as stale because it has not had activity in 6 months. It will be closed in 7 days if no further activity occurs. Allowing issues to close as stale helps us filter out issues which can wait for future development time. All issues closed by stale bot act like normal issues; they can be searched for, commented on or reopened at any point. If you'd like a closed stale issue to be considered, feel free to either re-open the issue directly or contact a developer. To extend the lifetime of an issue please comment below, it helps us see that this is still affecting you and you want it fixed in the near-future. Extending the lifetime of an issue may cause the development team to prioritise it over other issues, which may be closed as stale instead.

[github-actions[bot]]

This issue has been automatically marked as stale because it has not had activity in 6 months. It will be closed in 7 days if no further activity occurs. Allowing issues to close as stale helps us filter out issues which can wait for future development time. All issues closed by stale bot act like normal issues; they can be searched for, commented on or reopened at any point. If you'd like a closed stale issue to be considered, feel free to either re-open the issue directly or contact a developer. To extend the lifetime of an issue please comment below, it helps us see that this is still affecting you and you want it fixed in the near-future. Extending the lifetime of an issue may cause the development team to prioritise it over other issues, which may be closed as stale instead.

[github-actions[bot]]

This issue has been closed automatically. If this still affects you please re-open this issue with a comment or contact us so we can look into resolving it.