Fixing rememberable strategy.

The rememberable strategy was broken because we clear the
session/cookies before going to the second step so the remember_token
was being cleared from the cookies.
In this commit I make sure the remember me option is respected when
the second step is completed.

Ref #10
Version 1.4
add authy-form class
Add support for the authy-form to the SASS version of the css.
Bump version to 1.5
Correctly return to the previous url.

Before this commit it wasn't redirecting the user to the correct url
after signing in.

Fixes #12