drop autotools, use meson exclusively

Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>

TLS support

Fingerprint is avaialble as CertificateFingerprint property, the format is the
same as produced by GnuTLS' certtool, eg:

   sha1:d7860c6978d714e9e8f9805065602ea14e295df9

mconnect's certificate is accessible as Certificate property of
org.mconnect.DeviceManager interface on /org/mconnect/manager object.

Display device certificate when running show-device in verbose mode. To
introspect the certificate run the following:

    mconnectctl show-device --verbose /org/mconnect/device/0 | \
      certtool -i

Previous version of mconnect did not have a 'certificate' key in device section.
When loading such device do not fail instantly but rather log a warning and let
the loading continue further.

Glib TLS support is required to run some of the tests

The code will now generate the private key and certificate during startup.
There is a potential incompatibility with previous releases and the user may
need to unpair the device (in KDE Connect app) and pair again.

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.