Added support for phantomjs command line options

I needed to be able to run wraith with `ignore-ssl-errors` phantomjs option set to `true` as one of the domains I wanted to compare has an invalid SSL certificate. To do this I added a `phantomjs_options` key to the config file.

Usage example:

```yaml
phantomjs_options: "--ignore-ssl-errors=true"

domains:
...

screen_widths:
...

paths:
...
```