Improve markup and style sheets

* Fixes inconsistency with input wrapper classes.
* Improves markup for secondary links. Adds sign in link to sign up form
  for better navigation.

https://github.com/thoughtbot/clearance/pull/252
Add "#clearance" wrapper to markup
Prepare Clearance for Rails 4

* Change routes to use `get` instead of `match`.
* Don't allow multiline strings for email format.
* Rails 4 issues an exception when validates_format_of encounters regex
  that uses ^ and $ rather than /A and /Z. See this pull request:
  https://github.com/rails/rails/pull/6569
* `sign_out` should use DELETE, not GET.
* Remove irrelevant spec for testing regex.
* Test against latest security-patched Rails versions.
Persis BCrypt password during SHA1 migration

A full description of the issue this resolves is here:

https://github.com/thoughtbot/clearance/issues/236
Improve readability of locales
Improve UX of password reset

As reported on:

https://github.com/thoughtbot/clearance/issues/250

By default, the text on the password reset page read:

> We will email you a link to reset your password.

This implies that the system is already in the process of sending an
email,
and that no further action is required by the user. We have had multiple
users of our application fail to complete the password reset flow
because of
this confusion.

Here's how these users got stuck:

* Visit the login page.
* Enter their email address and an incorrect password.
* The application denies login with "Bad email or password" error.
* User gives up and clicks "Forgot password?" link.
* Reset password page loads with the text "We will email you a link to
 reset your password.". User thinks they are done. (After all, they
 already provided their email address on the login page.)
* User never completes the reset password form. Telephones support
 complaining their password is not being reset.

Our fix was to change the password reset text to:

> To be emailed a link to reset your password, please enter your email
> address.