GPR and LiDAR Tutorial

[aaarendt]

• check snowexdb usage and ensure it is using most up to date version
• condense some of the pramble text (reduce the background context, reference lists, etc)
• tidy up the commented code for looking at different sites. Develop more elegant way to explore multiple sites.
• test functioning of the rest of the code
• should we keep the discussion questions, or modify / reduce?