[1a] Add ids to token and segment links and pick ties by rule #430

Part of Phase 1 (#424) of the data layer plan.

Ids on token and segment links; the reducers and the PT9 converter write them; a saved interlinear project with any link that has no id loads as empty, as does each draft book holding one, with a log entry; the reducers pick approval ties and merge survivors by rule, not list order.

Done when: every new link has an id, approval ties and merges pick the same record whatever the list order, a new PT9 import and its editable copy keep their analyses through save and reload, and old data loads empty without error.

Depends on: #407 (done).

From the plan

Risks