Migrate install rewriting to new rewriters

[mattbucci]

Closes:

• https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/46
• https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/47
• https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/48
• https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/49
• https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/50
• https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/51

Fresh install is now working, but some warnings present. See https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/issues/52