Fix Bug 1058259 - notification 'warning' class conflicts with Custom CSS

Defined border-width and link styles with more specificity here to over-ride the customCSS ones on .warning

Couldn't bring myself to add it to the customCSS as suggested on the bug. It's more maintainable here and will get minified etc.
Merge pull request #2707 from stephaniehobson/1058259-warning-class-conflict

Fix Bug 1058259 - notification 'warning' class conflicts with Custom CSS
Bug 1054558: Notification after successful connect

If a user tries to authenticate with a service that is not already
associated with their account (for example, GitHub) they might be
notified that there is already an MDN profile using the same email
address. When this happens, the user is given the option of
authenticating with a third-party service that /is/ associated with the
account (for example, Persona) to make both services (in this case,
GitHub and Persona) authentication options for that account.

These changes notify the user when this is done successfully.
Merge pull request #2719 from openjck/1054558-account-association-feedback

Bug 1054558: Notification after successful connect