bskyweb: basic i18n setup

Uses Cookies, then HTTP Accept-Language, then default, to negotiate
language setting.

The cookie name is 'lang', and the value can be any string which would
be valid in Accept-Language. This includes a trivial 2-char ISO code.

Language setting is returned as 2-char ISO code (though could be
more flexible in the future if needed).

HTML language is configured (attr), and a secondary per-language
scripts.html file is included.

As a hack Makefile generates the scripts_*.html files; typescript build
system will need to populate those appropriately as part of 'make
build-web' to finish integration.

bskyweb/.gitignore

@@ -9,6 +9,7 @@ static/js/*.js
 static/js/*.map
 static/js/*.js.LICENSE.txt
 templates/scripts.html
+templates/scripts_*.html
 
 # Don't ignore this file
 !.gitignore