Plotting recipes for interferometer data

[anchal-physics]

• Added recipe to plot interferometer geometry on top of SOLPS mesh in the R-Z plane.
• Added recipes for plotting integrated and averaged electron density data from interferometer as time series.
• Added example file to see how to use these functions.

Plot outputs from the example file:

R-Z plane interferometer line of sight plot

gr()           # Fast and can save pdf
plot(space)
plot!(ids.interferometer) # Default plot_type is :los 
plot!(legend=true)

Integrated electron density vs time

gr()           # Fast and can save pdf
plot(ids.interferometer, plot_type=:n_e)

Average electron density vs time

gr()           # Fast and can save pdf
plot(ids.interferometer, plot_type=:n_e)

This completes the last two tasks in ProjectTorreyPines/FusionSyntheticDiagnostics.jl#1 and will complete the issue.

[eldond]

The example notebook runs.
The ugly part of the mesh is because of a bug in SD4SOLPS that has been fixed on branch mesh_ext_refined, so it is not a concern and shouldn't block this development.