Use Feura Sans font for the mobile layout.

fixes #3430
Put a nice Persona icon next to an email address if there is only one.
Add a little Persona icon next to the email addresses in the email picker when in mobile mode.

partial fix for issue #3410
Update the persona watermarks with high res versions.

rename email_input_blurred_bg=>persona_watermark
rename email_input_blurred_selected_bg=>persona_watermark_dark
Update styles as per Michael Maslaney and Maureen Hanratty's suggestions.
Remove the duplicate .buttonrow a, it was messing with Android 2.2/Android 2.3 browsers and causing the cancel button to be blue.
fixes #3446
Merge pull request #3441 from mozilla/issue_3430_feura_sans

Use Feura Sans font for the mobile layout.
Add an active/focus state on mobile buttons.
Use correct sized images for the persona watermark in the email picker

This is to get rid of the anti-aliasing rendering artifact that displays on scaled images in FirefoxOS.
Merge pull request #3444 from mozilla/issue_3410_email_picker_icon

Issue 3410 styling updates