refactor(client): Asynchronous rendering!

* Asynchronous can be used to check for prerequisites/errors before printing the template, preventing flashes of content before being fully ready.
* Only show the contents of the new screen once all async operations are complete.
* Add fxa-client.js->isSignedIn to check if a user is signed in with the given token.
* Move fxaClient creation from form.js into base.js so that authentication can be checked.
* Clean up base.js->render and the isSignedIn check.
* Update all the vew tests to expect async rendering.

issue #788
chore(client): Cleanup based on comments.

* Remove invalid comment
* Reorder functions to make review easier
fix(server): Ensure fonts have cacheable URLs.

* Serve fonts statically until connect-fonts has its business in order.

fixes #384
feat(client): updating js client to 0.1.18
Merge pull request #899 from vladikoff/js0.1.18

feat(client): updating js client to 0.1.18
Merge pull request #890 from mozilla/issue-788-async-render

refactor(client): Asynchronous rendering!
Merge pull request #895 from mozilla/issue-384-cache-fonts

fix(server): Ensure fonts have cacheable URLs.
fix(client): Enable back button functionality when visiting `/`.

* use history.replaceState instead of history.pushState when redirecting from `/`.

fixes #763
Merge pull request #897 from mozilla/issue-763-redirect-on-startup

fix(client): Enable back button functionality when visiting `/`.

@nchapman gave the r+, I rebased. Merging.
feature(client): Add a `/cookies_disabled` page.

* Add a cookies_disabled template, view, and test. Provides a link to SUMO to get help as well as a "try again" button.
* Split off most of the code from main.js into lib/start-app.js so that it can be tested.
* Split off config loading into its own modules, lib/config-loader.js so that it can be shared.

fixes #738
fix(build): Fix the typo when copying fonts.

fixes #907
fix(client): Fix disappearing error messages when toggling password visibility.

fixes #903
fix(client): Correctly handle the THROTTLED error from fxa-client.js->signUp

fixes #905
chore(client): Email addresses should not be bold.

fixes #902
feature(client): Add backoff protocol error strings.

* Use the 201 errno as the indicator for `server busy`
* Change `Service unavailable` to code 998, this is a client side only number.

fixes #484
Merge pull request #908 from mozilla/issue-907-typo

fix(build): Fix the typo when copying fonts.
Merge pull request #898 from mozilla/issue-484-backoff-buster

feature(client): Add backoff protocol error strings.
Merge pull request #884 from mozilla/issue-738-cookies-disabled

feature(client): Add a `/cookies_disabled` page.
Merge pull request #911 from mozilla/issue-902-delicate-settings-email

chore(client): Email addresses should not be bold.
Release v0.10.0