chore(metrics): Round timestamps to the nearest hour instead of day.

* This allows us more granularity when querying the metrics DB, without sacraficing user privacy.

fixes #1602
fix(signin): cache credentials for desktop sign-ins, otherwise only cache email

Fixes #1621.
Merge pull request #1629 from mozilla/issue-1602-one-hour-metrics-timestamp

chore(metrics): Round timestamps to the nearest hour instead of day.
Merge pull request #1626 from mozilla/issue-1621-fully-logout

fix(signin): cache credentials for desktop sign-ins, otherwise only cache email

r=ckarlof,nchapman,vladikoff
Release v0.21.0
tests(oauth): fix cached credential tests for oauth sign in
Merge pull request #1633 from mozilla/fix-oauth-tests-cached-creds

tests(oauth): fix cached credential tests for oauth sign in
chore(docs): Update README instructions

[skip ci] Fixes #1631
Merge pull request #1634 from vladikoff/issue-1631-readme

chore(docs): Update README instructions
tests(signin): make cached credential tests more stable
Merge pull request #1636 from mozilla/improve-cached-creds-functional-tests

tests(signin): make cached credential tests more stable
Revert "tests(signin): make cached credential tests more stable"
Merge pull request #1638 from mozilla/revert-1636-improve-cached-creds-functional-tests

Revert "tests(signin): make cached credential tests more stable"
tests(signin): make cached credential tests more stable
Merge pull request #1641 from mozilla/improve-cached-creds-functional-tests-2

tests(signin): make cached credential tests more stable
tests(webdriver): Update Selenium version
refactor(client): Create one FxaClient and one Relier in app start.

* Remove the singleton FxaClient created in views/base.js, instead create one in app-start and pass it via the router to all objects that need it.
* Update assertion.js to use a passed in fxaClient instead of creating its own.
* Update the tests that need to be updated.

Part of issue #1623
Merge pull request #1644 from vladikoff/sel243

tests(webdriver): Update Selenium version
chore(tests): Insert a Relier into each test instance of FxaClient and View
Merge pull request #1645 from mozilla/issue-1623-refactor-fxaclient-relier-creation

refactor(client): Create one FxaClient and one Relier in app start.