qt: additional options

Adds an additional option to build with OpenSSL, although I’d be strongly in favour of us making that recommended rather than optional. It seems to opportunistically link into OpenSSL if it’s available during the compile stage, so I’d be in favour of moving to a more secure default by forcing it to link to our OpenSSL rather than grabbing one when it wants to, which is very likely to be the defunct system version.

```
OpenSSL support ........ yes (run-time)
```

I’d also like to change the d-bus optional dependency to recommended, as Debian ship it as a [mandatory dependency](https://packages.debian.org/sid/libqt4-dev), and the additional library is small enough that including it isn’t overly taxing on users, compared to forcing anyone who wants to use the d-bus link to rebuild qt manually which can take anything between 1-2 1/2 hours per compile.