fix(eighth): distribute students evenly within capacity

[tonymac129]

Proposed changes

• Option to toggle allow exceeding activity capacities when distributing evenly
• Students are distributed evenly across selected activities when possible (either within all activities' capacities or when allow exceeding capacities is checked )
• If some of the activities have a smaller capacity, students are still distributed evenly for the rest
• Improve checkbox behavior and prevent a student from being assigned multiple activities

Brief description of rationale

• Better calculates student distribution and tries to distribute as evenly as possible
• Improves UX
• Closes Fix "Distribute Students without Signups" Function #1300

[tonymac129]

I don't know why the tests keep failing, could it be because the distributing behavior changed?

[coveralls]

coverage: 78.625% (+0.007%) from 78.618% — tonymac129:fix/distribute-students into tjcsl:dev