Support downloading from secure SSL/HTTPS links / Build cmake's libcurl with SSL support

The error is pretty clear: `libcurl was built with SSL disabled, https: not supported!`

I can download fine from a standalone curl, the problem is from RosBE's cmake and its statically linked libcurl. This is problematic as I'm using `file(DOWNLOAD ...)` for downloading the root CA certificates from Mozilla, and downloading them from plain HTTP would be silly.

I have included an example script, which can be executed with `cmake -P ca-cert-mozilla-download.txt`.