Patch/course capacity per section

[Russell-Waterhouse]

Refactors FE course model and Alg course models to have maxCapacity Refactors FE course model to have fall_sections, spring_sections, summer_sections as many-to-many attributes.

Big thanks to Raph and Ben for help with this PR!

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Added to this branch after it went up for PR initially:

• Course & Section serializers update for FE + unit tests
• Algorithms packages versions bumped to latest
• Entire merge of PR #123 into this branch - handles merging of unmerged time intervals for preferredTimes field
• Minor typo in Professors CSV data removed

[rbassot]

Integrations: The state of this branch after the most recent commit has passing integrations with respect to the Algorithms teams of both Company1 and Company2 (us).