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.
feat(metrics): Log `entrypoint` to the metrics.

* Add the FxDesktopRelier that imports `entrypoint` and `context` from the URL.
* Relier extended to import `service`, `redirectTo`, `client_id`, and `state`
* Initialize either the FxDesktopRelier or normal Relier on startup.
* Instead of Metrics importing values directly from the URL, they are fetched from the Relier and passed in on creation.

fixes #1568