Convert CTA links to blue

[stephaniehobson]

We'd like to back-port the blue CTA links used on FFFY and firefox/accounts in to Protocol.

Here's the code from FFFY:

    .mzp-c-cta-link {
        &:link,
        &:visited {
            color: $color-link;
            border-bottom-color: $color-link;
        }
        &:hover,
        &:focus,
        &:active {
            color: $color-link-hover;
            border-bottom-color: $color-link-hover;
        }
    }

[stephaniehobson]

Fixed in #282