[settings] Apply proxy on dcrd/dcrwallet

[bgptr]

Before this, proxy settings determine only links/API calls.
This diff applies proxy settings to dcrd and dcrwallet too, when the proxy type is SOCKS 5. With this, users can configure dcrd/dcrwallet as a Tor client.
It changes the proxy settings view a bit too:

• After changing the proxy settings, the daemon and wallet need to restart after confirmation.
• Since the proxy type and location values are firmly related, the submit event does not trigger automatically, but by clicking on a dedicated submit button:

Tests updated also.