Swath bathy from sl3 and 2D EGN correction

[CameronBodine]

Is your feature request related to a problem? Please describe.
Not a problem. Add support for sl3 swath bathy.

Describe the solution you'd like

• Allow for export of swath bathy (X,Y,Z point cloud and/or raster surface) from sl3 files.
• Create 2D EGN correction (beam angle and range) using the swath bathy. First described in this issue.

Describe alternatives you've considered

• Use existing SL3Reader. Adding functionality to PINGMapper would continue to improve and add features for existing users.

Additional context

• SL3Reader companion manuscript