PHP 7.0 compatibility

If you get any errors after changing to PHP 7.0 just check the following issues.

127.0.0.1 instead of localhost for mysql connections

PHP 7.0 connections to localhost are not working using PDO. Instead you need to change the database host to 127.0.0.1
You also need to make sure that the mysql user has permissions via 127.0.0.1.