media-session: add bluez-autoswitch module

Add module that switches bluez device profile to HFP/HSP if an input
stream (non-monitor, autoconnect) appears, and the current default
output device is bluez one that does not have input route.

When all input streams are gone, switch all changed profiles back.

Pending restore state is saved to session manager state files, in order
to restore it if e.g. devices get disconnected.  This usually is not
currently necessary since the bluez5 plugin prefers to connect to A2DP
over HFP, but might matter in future with backchannel-enabled A2DP
codecs.