When sharing URLs through KDE Connect, the incoming "url" usually contains some
additional description that was added by the source application. Use regext to
pick up any valid http[s] URLs that may be found in the text.

Replace OpenSSL helpers with ones based on GnuTLS. GnuTLS is already an indirect
dependency since we require GLib's TLS support. As support for older protocol
versions was removed, we will not need any extra library for handling explicit
packet decryption.

This change will also resolve potential license incompatibility issues.