Replace `android_id` with `student_id`

[jo-elimu]

Description

Replace Android ID with Student ID in UI and CSV exports.

• Redact Android IDs
• Generate Student ID during data collection (*ImportScheduler.java)
• Display Student ID in Analytics dashboard (/analytics)
• Remove Android ID from CSV exports (learning events & assessment events)

Why?

See parent issue

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• Depends on Add Word ID to WordLearningEvent #2113
• Depends on Add WordAssessmentEvent #921

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