feat(server): Add a forwarding proxy for IE8.

* Proxy auth server requests when the url is prefixed with `/auth`
* Proxy oauth server requests when the url is prefixed with `/oauth`
* Show the user a `Service unavailable` error if the proxy request fails.

Other info:

* The oauth proxy tests are disabled until we have an OAuth server set up.

fixes #102
Disable the IE8 proxy in production.

* Add configuration items (fxaccount_proxy and oauth_proxy) to enable/disable the proxy.
* Add /config tests to ensure proxy URLs are returned for IE8
fix(tests): Make IE10/IE11 pass all the mocha tests.

* IE10 passes with no additional work.
* IE11 requires mouse interaction for the tests to complete correctly.

issue #1334
feat(metrics): Log which marketing material is shown to a user.

* Add `marketingType`, `marketingLink`, `marketingClicked`.
* `marketingType` is either `android-sync` or `survey`
* `marketingLink` is the URL that the user can click on.
* `marketingClicked` is whether the user clicked on the marketing.

fixes #1259
bug(rtl): fix inputs on RTL locales
feature(styles) animation timing variables
Merge pull request #1364 from mozilla/issue-1361

feature(styles) animation timing variables
Merge pull request #1360 from mozilla/issue-1341

bug(rtl): fix inputs on RTL locales
Merge pull request #1357 from mozilla/issue-1259-promotion-metrics

feat(metrics): Log which marketing material is shown to a user.
Add a TODO to enable OAuth tests with #1246
Only gather entropy from the server if the browser does not support crypto.getRandomValues.
Merge pull request #1308 from mozilla/issue-102-proxy-auth-oauth-ie8

feat(server): Add a forwarding proxy for IE8.
Merge pull request #1355 from mozilla/issue-1334-ie-test-failures

fix(tests): Make IE10/IE11 pass all the mocha tests.
refactor(client): Remove global variables in fxa-client.js

* Replace the global variables in fxa-client.js with instance variables.
* All view tests create their own fxa-client to avoid cross test pollution.
* One fxa-client instance is shared across views for the application.

Work done as part of the evaluation of the amount of work to replace fxa-js-client with a mock for testing. (See #1356)

fixes #1304