Fix including http:// in the proxy URL:
The proxy host parsed incorrectly, when it was typed with a scheme (http or https).
Now proxy can be specified with the scheme.

Fix invalid type conversion:
m_proxyPort converts to its ASCII representation.
Use `QString::number` to include a proxy port properly.

Issues:
https://github.com/ariya/phantomjs/issues/11117
https://github.com/ariya/phantomjs/issues/10811