feat(metrics): Add metrics for signup, preverified signup, signin, hide the resend button.

Add:
* signin.success- for a user who signs in successfully.
* signup.preverified - for users who attempt to sign up with a preVerifyToken
* signup.preverified.success- users who successfully sign up with a preVerifyToken
* signup.success - users who successfully initiate a signup.
* oauth.signin.success- for an OAuth user who signs in successfully.
* oauth.signup.preverified - for an OAuth user who attempts to sign up with a preVerifyToken
* oauth.signup.preverified.success- for OAuth users who successfully sign up with a preVerifyToken
* oauth.signup.success - for OAuth users who successfully initiate a signup.
* confirm_reset_password.resend - users who attempt to resend the password reset email.
* confirm_reset_password.too_many_attempts - when we hide the "Resend" button for password reset users who have tried too many attempts.

Also:
* Hook up the debounce code to the password reset.
* Add a base.js->logScreenEvent that logs an event using the screen name as the prefix.
* Change `/` in screen names to `.`
** `screen:legal/tos` => `screen:legal.tos`
** `screen:legal/pp` => `screen:legal.pp`
** `screen:oauth/signup` => `screen:oauth.signup`
** `screen:oauth/signin` => `screen:oauth.signin`

issue #1559
fixes #1147
Merge pull request #1745 from mozilla/issue-1559-metrics-updates

feat(metrics): Add metrics for signup, preverified signup, signin, hide the resend button.

I see this quote: "I'd say it's good to go once rebased." Rebase is done. Merging.