PSR-12 compliancy

This reverts commit 6bcea51e.

Bugfix. While SimpleSAML\Database::query() returns a PDOStatement, SimpleSAML\Database::exec() doesn't. Make both return an integer with the amount of rows affected. Add a return value to SimpleSAML_Metadata_MetadataStorageHandlerPdo::initDatabase().

(being respectful with occurences that might change the behaviour, i.e. default database prefixes)

Move the DatabaseTest to tests/lib/SimpleSAML/ where it belongs. Reformat code. Fix a few issues with phpdoc. Removed some unused variable. Use typed methos from SimpleSAML_Configuration instead of getValue().