organize registration dates by term, not semester

[jyn514]

this is the reason that parse_semester currently barfs all over the terminal; it assumes semesters are the same for each class and gives a (loud) warning if this is not true. it should instead assume terms are all the same.

example: first-semester fall 2013 is a unique term (where all fields are the same), but fall 2018 is not, because you could have either first- or second- half semester classes

[jyn514]

reconsidering semesters at all, the only common attribute is registrationEnd, we may as well make it a part of term

[jyn514]

aggggh - the term is not actually a part of the info sent by the server. We do have the semester, maybe we could have the first and last start dates as columns in the semester and infer terms from there? (i.e. starts on first day, must be first half; ends on last day, must be second half; does both, must be full term)

[jyn514]

not on section link either

[jyn514]

this will work. If we use a set instead of dictionary (i.e. no primary key), we just add every term from every section and hope that most are duplicates.

We need a primary key to link sections back to term. We'd have to make an arbitrary key, the same way SQLite does ROWID

[jyn514]

As an alternative, the school separates by term internally, they just don't send the info over the web. We could download one class from each term and see what the dates are there, then download in bulk.

The downside to this is that

• downloads already take forever, we have a lot of files on disk and I'm getting reluctant to add more
• we won't know if we've assumed wrong and terms do not have the same dates

[jyn514]

done in https://github.com/jyn514/GradeForge/commit/1169cc359a1b0b1a4354cea77c6133b13d335ff5