Add PHP 5.5.18 and allow additional configure params on PHP builds

To add configure params to a PHP version, instead of this:
```
include php::5_5_18
```
Do this:
```
php::version { '5.5.18-zts':
  version => '5.5.18',
  configure_params => '--enable-maintainer-zts'
}
```

This does not allow multiple variants of the same version of PHP to be installed. i.e. you can't install 5.5.18 and 5.5.18 with ZTS.