Add OFLocalization

This singleton gives access to all things locale, including the ability
to get localized strings.

This also adds the OF_LOCALIZED() macro. Its first argument is an ID for
the string to be localized and its second argument is the fallback
string to be used if it cannot retrieve the localized string. Following
that are variable name / value pairs to be replaced in the localized
string.

Getting translated strings is not implemented yet: Instead, it always
uses the fallback string.

This also switches ofhttp to localized strings.