JB#44692: Add support for wpa_supplicant blobs of inlined cert data

See merge request !4

  gsupplicant_bss_remove_all_handlers
  gsupplicant_interface_remove_all_handlers
  gsupplicant_network_remove_all_handlers
  gsupplicant_remove_all_handlers

Compatibility with glib 2.56

See merge request !3

Handle "notify" instead of "g-properties-changed". It's advertised
by glib docs as the right way of doing it.

If the stubs are generated by gdbus-codegen < 2.56 then strv getters
return shallow copy, i.e. the return result should be released with
g_free(), but the individual strings must not be modified. Luckily,
this can be determined at compile time.

See https://bugzilla.gnome.org/show_bug.cgi?id=770335

Don't rely on gutil_types.h to pull it in.

Maintain the list of connected stations

See merge request !2

This adds 'stations' field to GSupplicantInterface

This is primarily to make gsupplicant_util.h gio-free

Treat SSIDs consisting of all zeros as empty

See merge request !1

Not much can be unit-tested though

Avoid using g_variant_get_data_as_bytes and g_hash_table_get_keys_as_array

Invalid read of size 4
   gsupplicant_interface_add_network_call_free (gsupplicant_interface.c:1148)
   gsupplicant_interface_add_network_call_free1 (gsupplicant_interface.c:1167)
   g_source_callback_unref (gmain.c:1561)
   g_source_destroy_internal.constprop.8 (gmain.c:1207)
   g_main_dispatch (gmain.c:3177)
   g_main_context_dispatch (gmain.c:3769)
   g_main_context_iterate.isra.4 (gmain.c:3840)
   g_main_loop_run (gmain.c:4034)
   main (main.c:866)
 Address 0x5457f2c is 28 bytes inside a block of size 52 free'd
   free (vg_replace_malloc.c:530)
   gsupplicant_interface_add_network_call_free (gsupplicant_interface.c:1159)
   gsupplicant_interface_call_add_network_finish (gsupplicant_interface.c:1185)
   gsupplicant_interface_add_network4 (gsupplicant_interface.c:2559)
   _g_closure_invoke_va (gclosure.c:867)
   g_signal_emit_valist (gsignal.c:3294)
   g_signal_emit (gsignal.c:3441)
   gsupplicant_network_signal_property_change (gsupplicant_network.c:158)
   gsupplicant_network_emit_pending_signals (gsupplicant_network.c:196)
   gsupplicant_network_proxy_created (gsupplicant_network.c:477)
   g_task_return_now (gtask.c:1107)
   ...