Display issue in the Databases/Database Users section

Four anomalies are observed in the validation of the Databases and Database Users forms. They concern only the display of error messages or the translation strings.

Coding issue

1. Duplicate message (database name)
   The key database_name_error_empty (Database name is empty) is displayed twice when creating a database.

Explanation issues (strings / announced limits)

1. Incorrect announced maximum length for database names
   The announced maximum length (64) is incorrect: the actually usable length is 63 characters (prefix included), due to the required string terminator (\0).
   Affected keys: database_name_error_len and database_user_error_regex.
   
   
2. Inappropriate text and limits for database usernames
   The key database_user_error_regex (Invalid database user name. The username may contain these characters: a-z, A-Z, 0-9 and the underscore. Length: 2 - 64 characters.) reuses the constraints of database names, whereas database usernames are subject to a shorter limit.
   
   
   
3. Incorrect announced maximum length for database users
   The announced maximum length (32) is incorrect: the actually usable length is 31 characters (prefix included), for the same technical reason (\0).
   Affected keys: database_user_error_len and database_user_error_regex.