Add working script to clean data

[annychih]

The new clean_data.py script works! Hooray!

Notes:

• This file satisfies our Milestone 2 requirement to have at least one working python script.
• I've saved one of the outputs of running this script to the data folder (called "clean_data.csv"); this is the file you'll want to use for your plotting functions.
• For plots made to compare 'Aboriginal' and 'Non Aboriginal' students, you'll want to have arguments in the function that specify these subgroups and then filter based on them within the plotting function itself.
• Plotting functions that compare just 'BC PUBLIC SCHOOL' and 'BC INDEPENDENT SCHOOL' don't need to filter the clean_data file because it only includes school-level data (i.e. the rows with totals have been dropped).

[robilizando]

Good job, I merge your request and start using this file. Thanks