peerdiscovery: add getNearbyPeers() function

bin/dbus/cx.ring.Ring.ConfigurationManager.xml

bin/dbus/dbusconfigurationmanager.cpp

bin/dbus/dbusconfigurationmanager.h

configure.ac

src/account.h

src/client/configurationmanager.cpp

src/dring/configurationmanager_interface.h

src/jamidht/jamiaccount.cpp

src/jamidht/jamiaccount.h

src/manager.cpp

src/manager.h