feature(client): debounce resend button clicks.

* Send emails on the first and forth attempt. Shake the success message otherwise.
* After the forth attempt, hide the resend button for 5 minutes.
* Change the name of `.error-shake` to `.shake`.
* Update `.shake` to cause 8px of movement, not 100px.

issue #885
Merge pull request #1005 from mozilla/issue-885-debounce-resend-email

feature(client): debounce resend button clicks.