Fix unverified users not being able to sign in

Even if an email address is marked unverified, a user should still be able to sign in with the address. Once the user signs in, they will be forced to verify their ownership of the address.
Add tests to ensure password reset reverification works as expected from both the auth screen and the email picker.
Remove "Persona" from the password reset email

fixes #3790
Set the font size on the loading screen to 14pt with 22px of line-height

fixes #3636
Merge pull request #3821 from mozilla/issue-3811-unverified-signin

Issue 3811 unverified signin
Merge pull request #3823 from mozilla/issue_3790-email-titles

Remove "Persona" from the password reset email
Merge pull request #3824 from mozilla/issue_3636-loading-screen-type

Set the font size on the loading screen to 14pt with 22px of line-height
Update mobile button styles to match those specified on the FirefoxOS style guide.

fixes #3635
Remove extraneous (and incorrect) border-radius

Fixes #3814
Set the header nav radius to be a consistent 7px

Fixes #3813
Sign into » in to, and Simplified » Simple
Merge pull request #3830 from chilts/issue-3814

Remove extraneous (and incorrect) border-radius
Merge pull request #3831 from chilts/issue-3813

Set the header nav radius to be a consistent 7px
Merge pull request #3832 from mozilla/issue_3635-mobile_button_styles

Update mobile button styles to match those specified on the FirefoxOS style guide.
Merge pull request #3833 from ryanfeeley/dev

Language tweaks: Sign into » in to, and Simplified » Simple