Don't write a new db state entry for a reloaded task proxy.

This results in an IntegrityError for reloaded waiting task proxies
(error is caught and converted to an update, but printed to stdout).
Carry over db_queue to reloaded task proxies.
Record db state at non-reload task init.
Treat restart and reload the same in task proxy init.
Retrieve db ops for all tasks, incl runahead pool.
Split handling of task messages and db ops.
Enforce explicit use of tasks in the runahead pool.
Fixed two runahead tests.
#1211: fix cylc show fine-level clock triggered
Log db retries and operation being tried.
Don't reset tasks in final states to held in held suites.
Review feedback change.
Add comment line.
Log database being retried on.
Merge pull request #1233 from arjclark/suite_db.log_retries

run db: Log db retries and operation being tried.
Merge pull request #1234 from arjclark/reload.fix_held_reset

held suites and reload: Don't reset tasks in final states to held in held suites.
 #1224: fix graphing for start-up task line.
Merge pull request #1236 from benfitzpatrick/1224.fix-graphing-standalone-initial-task

Fix graphing for start-up task line.
Test #1221
Fixed two runahead tests.

They previously depended on task proxies from the runahead pool not having
entries in the run db.