update wideband beam-steerable reflectarray notebook

[dmarek-flex]

This notebook needs overall more polish and addition of the remaining steps for simulating the entire completed reflectarray.

Subtasks;:

• switch to layer refinement specs, instead of mesh overrides and snapping points
• add steps for simulating the horn excitation
• add steps for constructing the binary phase mask for the reflectarray
• add steps for simulating the final reflectarray