view: add --scalebar-linewidth option

[yunjunz]

Description of proposed changes

• view: add --scalebar-linewidth option

• prep_gamma: fix the inps.sensor.lower() issue when sensor is not specified, i.e. inps.sensor is None, by shifting the lower() operation inside extract_metadata4interferogram()

• asc_desc2horz_vert.get_design_matrix4east_north_up(): add type checking for the obs_direction arg.

Reminders

• Pass Pre-commit check (green)
• Pass Codacy code review (green)
• Pass Circle CI test (green)
• Make sure that your code follows our style. Use the other functions/files as a basis.
• If modifying functionality, describe changes to function behavior and arguments in a comment below the function declaration.
• If adding new functionality, add a detailed description to the documentation and/or an example.