…toolbox#543)

* Added exp backoff when submission failed attempt

* Some cleanup

* Exponential backoff tests and refinements

To aid understanding the existing code and support these changes, `uploadQueue` has been converted from `Promise`s to `async`/`await`.

- Adds tests for retry-specific behavior, and related behavior affected by these changes

- Renames some properties/variables in exponential backoff to be more explicit/clear

- Corrects the retry delay calculation. It previously would retry immediately after initial failure

- Moves all retry/timing logic into exponential-backoff.js. It previously implicitly depended on a session-global `setInterval` long-polling call in records-queue.js. Being session-global, its timing relative to the exponential backoff itself would be unpredictable

- Attempts to upload existing queued records on page load, immediately after determing whether there are queued records to upload

- Cancels retries/backing off when the user attempts to submit a record

- Initiates retries when offline as determined by `connection.getOnlineStatus`

- Cancels retries/backing off when connectivity is restored, as determined by `connection.getOnlineStatus`

* Retry submission on partial failure

* Fix: offline-capable upload messaging consistency

- Consistently display success banner, whether on load, user submission, or post-backoff success

- Consistently display failure alert whether caused by being offline or a non-auth error

- Display dialog for auth error, with wording updated to reflect queueing success (rather than warning about losing unsaved data, as there should not be at submission time)

---------

Co-authored-by: Anji Tong <anjitong@hotmail.com>

feat(app): add enketo namespace to all debug statements

Largely based on getodk/javarosa#707. The biggest divergence besides obvious language/API differences is the validation approach. And `@ts-check` was added to ensure the validation and types actually match the expected runtime values.

Prepare 6.1.0 release

Use Core version with performance optimizations

Make pdf generation timeout configurable

# Conflicts:
#	Gruntfile.js
#	app/controllers/transformation-controller.js
#	app/views/surveys/webform.pug
#	docs/tutorial-12-ordinals.html
#	package-lock.json
#	public/js/src/enketo-webform.js

…n last merge to custom OC controller

…t merge

…and probably other files)

… specs

… time)