Add support for "lockable" record edits

[Kris Deugau]

Locking (advisory or otherwise) will help prevent multiple concurrent changes from getting done badly and ending up publishing wrong data.

Concept: On clicking to edit, a token is pushed to an advisory table and flag is set in the session.

If the record is updated, the token is tagged for clearing in <n> seconds (60? can't be too short) after the event (to prevent unlock-update races) - other sessions can see the update time and show a warning with the "new original" record vs their new update.

If some other action is taken, the session flag and advisory token are cleared so other clients don't block.