plugin: add editable preference

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

bin/dbus/dbuspluginmanagerinterface.cpp

bin/dbus/dbuspluginmanagerinterface.h

bin/jni/plugin_manager_interface.i

configure.ac

meson.build

src/client/plugin_manager_interface.cpp

src/dring/plugin_manager_interface.h

src/fileutils.cpp

src/fileutils.h

src/plugin/jamipluginmanager.cpp

src/plugin/jamipluginmanager.h

src/plugin/mediahandler.h