Change Roundcube to use SQLite by default in new installs

Please switch the default storage for Roundcube to SQLite in new installs to reduce dependency upon MySQL/MariaDB.

At present to accomplish this manually, an administrator needs to set roundcube_db=sqlite in /root/cpanel_profile/cpanel.config prior to installing cPanel, similar to the following example:

1. mkdir -pvm0711 /root/cpanel_profile && echo -e "mysql-version=10.1\nroundcube_db=sqlite" > /root/cpanel_profile/cpanel.config

Please make using SQLite for Roundcube the default behavior in new installs.