Add specs for the account menu, downloads-as-offline-library, offline
downloaded-only filter, and scoped search (+ boundary revision). Add the
new UR/DR entries to requirements.md, update ux-flows, and regenerate the
traceability matrix.
TRACES: UR-049, UR-050, UR-052, UR-053, UR-054, UR-055, UR-056
dtourolle