Refactor TripReport model to be part of Trip model (#111)

[anorthall]

Refactor the TripReport model to completely remove it and integrate it into the existing Trip model to reduce code duplication and simplify views and templates.

All existing TripReports will be migrated to the relevant field in a Trip and privacy will be adjusted to the most conservative option if the TripReport privacy differs from that of the Trip it migrates to.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
app/core/logging.py	93.33% <100.00%> (+4.76%)	⬆️
app/logger/admin.py	97.61% <100.00%> (+0.95%)	⬆️
app/logger/factories.py	100.00% <100.00%> (+4.46%)	⬆️
app/logger/forms.py	100.00% <100.00%> (ø)
app/logger/mixins.py	84.31% <100.00%> (-4.58%)	⬇️
app/logger/models/__init__.py	100.00% <ø> (ø)
app/logger/models/trip.py	99.06% <100.00%> (-0.01%)	⬇️
app/logger/urls.py	100.00% <ø> (ø)
app/logger/views/__init__.py	100.00% <ø> (ø)
app/logger/views/userprofile.py	94.87% <ø> (ø)
... and 3 more

... and 1 file with indirect coverage changes

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