Dashboard keywords alignment for install & update

When updating to 5.6.0 or 5.6.1 page keywords are not the same as those set by a fresh install. Let's align them!

Please remark that there are t() functions in the upgrade files. Since the data (page names, page keywords, ...) should be stored in the db in en_US, I think we should also update the file /web/concrete/core/controllers/single_pages/upgrade.php to switch to en_US before executing the upgrade scripts (and obviously we should switching back to the previous locale when they finish).