Improve installer:

Improve installer:

* Use a superuser account (such as root), if specifed, to create tables
* Don't overwrite conservative permissions on the mySQL user with ALL permissions, if said user exists
* Changes to some of the wording of explanations for fields

This will pre-emptively fix an issue arising if the regular-use user doesn't have permissions to set up the schema, since the end-user must now indicate this and provide superuser account details. Follow-on from last night's fixing 921 et al.