Minor cleanup of combining basics exercise
Add optional challenges to combining the basics exercise
Add use of EcoData Retriever to scientific Python problem
Rename Numpy exercises to Scientific Python

This allows the problems to be tackled using either Numpy or Pandas
Re-title Numpy problems as Scientific Python
Updating links after Numpy -> Scientific Python renaming
Updating Writing Functions notebook to current version
Remove empty lecture on functions
Cleanup Scientific Python exercises (minor)