Add string context to "Strong" for translation

The string "Strong" is used in two different ways in core: To describe password strength (on /user/n/edit), and to describe font weight (on /filter/tips). In Norwegian, we need to translate strong-not-weak (password) differently from strong-to-describe-font-weight. (We call a strong font a "fat font" in Norwegian, but a "fat password" looks really weird.)

For Norwegian, the contexts "font weight" and "opposite of weak" are fine. But I guess other languages might have other needs. I'll drop a heads up about this issue in the translation mailing list and in http://groups.drupal.org/translations so people speaking other languages can join in.

Also, I don't know if we should add contexts to both variants of the string, or pick one as default and add context to all other meanings.

Background on string contexts: http://drupal.org/update/modules/6/7#locale_context
(I'll add the phrase "translation context" here as well, in case someone's searching for that. But "string context" seems to be the most frequently used phrase. I've added "string context" as issue tag, I guess we'll see more of these issues as more translators get their teeth into 7.x.)