Rework `clock` endpoint to hold multiple, future timeslots

• Rework clock endpoint to hold multiple, future timeslots
• Simplify structure as a result and per needs of meta#42

changed milestone to %1.0-alpha2 — Precise Pheasant

added P2 + 1 deleted label

assigned to @david

added To Do label

added Doing label and removed To Do label

mentioned in commit dashboard-clock@76c5aaa1

mentioned in commit engine@05122870

mentioned in commit e27eeabb

mentioned in commit 9b92e9f8

closed

removed Doing label

mentioned in commit engine@113e097a