Refactor Times to only encompass a single session of a course

[Purplegaze]

Proposed Changes

Initial refactor and migration script to change Times objects in the database to only encompass a single session of a course. second_room (currently unused due to a bug) is removed, first_room is renamed to location, and a new session field is added to disambiguate the F and S sessions of a year-long course. A fall-winter Meeting will now have two Times objects linked to it, one for each session.

This moves the database in line with the direct timetable API response, which splits the fall and winter timeslots of a year-long course into different objects, and is a precursor to fixing the bug where year-long (Fall-Winter Y session) courses don't appear in the database.

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Questions and Comments

(See separate comment)

[Purplegaze]

I'm unsure what the scope of this PR should be, and what I should add into a separate PR.
So far I've added the migration script and changed Times itself, and resolved any immediate errors in Tables.hs (i.e. Times to Time and Time' conversions) by temporarily slotting in null data. But there are other places in the code that expect Times to behave a certain way which I need to rewire (e.g. tests still pass, but the location doesn't show up at the moment). Time and Time' will also need to be changed to match, and in turn, everything that relies on them. What extent should I bring this PR to, and what should be separate?

[coveralls]

Coverage Report for CI Build 0

Coverage decreased (-0.06%) to 57.326%

Details

• Coverage decreased (-0.06%) from the base build.
• Patch coverage: 4 uncovered changes across 1 file (7 of 11 lines covered, 63.64%).
• 1 coverage regression across 1 file.

Uncovered Changes

File	Changed	Covered	%
app/Database/Migrations.hs	7	3	42.86%

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
app/Database/Tables.hs	1	31.48%

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Coverage Stats

Relevant Lines:	3950
Covered Lines:	2316
Line Coverage:	58.63%
Relevant Branches:	964
Covered Branches:	501
Branch Coverage:	51.97%
Branches in Coverage %:	Yes
Coverage Strength:	163.35 hits per line

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💛 - Coveralls

[david-yz-liu]

Hi @Purplegaze, you're definitely in the right direction here. For this task it'll be divided into multiple steps, so I've created a new branch on origin called y-course-refactor. As a first step, please re-make this PR, but using the target branch of Courseography:y-course-refactor instead of Courseography:master. You will continue to make other PRs onto that branch until we're done, at which point we'll make one file PR to merge y-course-refactor into master.