wizard: Remove plugins usage

It was used by a test plugin we ship ourselves for Geoclue 1.x,
and NetworkManager. Given that NetworkManager doesn't make use
of it anymore, let's remove it.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
wizard: Add "confirm" ret for PIN detection
lib: Add "device-removed" signal

This allows us to easily identify devices that were removed,
which listening to the model's row-deleted doesn't allow us to do.
lib: Remove plugins support

Unused by either the wizard or the settings panel.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Insert data straight away

The data is available, so insert the new devices with their values
straight away. This means that front-ends don't receive as many
signals, and that they don't have to filter out NULL names.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Print "default-adapter-discovering" when it changes

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Fix "default-adapter-discoverable" property

Which wasn't getting updated when the default-adapter changed.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Remove killswitch functionality

That code has now moved to gnome-settings-daemon's Rfkill interface.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Fix "default-adapter-name" property

Which wasn't getting updated when the default-adapter changed.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Make _set_discoverable() more efficient

Get the properties proxy directly from the adapter treepath.
This avoids an unnecessary search in the treeview.

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Remove deleted functions from symbols file

https://bugzilla.gnome.org/show_bug.cgi?id=719564
lib: Make bluetooth_client_get_connectable() private
lib: Remove GtkStock usage

As it is deprecated now.
lib: Simplify pairing agent API
lib: Clean ups to bluetooth_client_setup_device()
lib: Remove unused "path" argument when pairing
lib: Fix test-agent for API change
wizard: Update for BluetoothAgent API changes
lib: Make bluetooth_client_setup_device() GIO-style

Rather than using our custom callback that doesn't support
passing user_data.
wizard: Port to new _setup_device() API