Fix query and logic for retrieving a particular locale stats for acs-lang admin/index page. In particular, messages that do not exist in a certain locale are properly computed in order to calculate deleted and untranslated ones, at the price of executing one query per locale instead of just a big one.
Refactor acs-lang 'admin/index' page, adding the new columns 'total' and 'deleted' to the listing, and reworking the query so it is faster (53ms -> 7ms), correct (number of messages by state are computed coherently with other acs-lang pages) and gives more information