Add more statuses to for the grade loader #92

[SoggyRhino]

I felt like expanding the original approach to include "P", "CR", "NC", "I", "NF" would have been obnoxious so I changed to a map based approach.

"W", "P", "CR", "NC", "I", "NF" do not consistently appear between semesters so they are all optional and not guaranteed (just as W was before).

Some of the older semesters have an NF column so I included that as well. I have no idea what it stands for though so let me know if it should be removed or combined with another column.

The order is the same as the original but with the new grades added to the end. This means that all of the indexes on the front end should still work.

Old:
"A+", "A", "A-", "B+", "B", "B-", "C+", "C", "C-", "D+", "D", "D-", "F", "W"
New:
"A+", "A", "A-", "B+", "B", "B-", "C+", "C", "C-", "D+", "D", "D-", "F", "W", "P", "CR", "NC", "I", "NF"

[mikehquan19]

@SoggyRhino yeah the NF status is not really needed by Trends cuz it's old. So we can remove it.