LP1802593: Correct formatting of language code in Angularjs, KPAC

LP1802593: Correct formatting of language code in Angularjs, KPAC

EgWeb offers two different formats of the current locale: ctx.locale and
ctx.eg_locale.  This commit configures the lang attribute in AngularJS
staff client, OPAC, and KPAC to use eg_locale, since it has the
appropriate format (e.g. en-US, fr-CA).

Also adds some tests for EgWeb's handling of language codes.

Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>