dispatcher-connection: new dispatcher for connection status scripts

The user or the packages can install custom dispatcher scripts that
will be run by the ModemManaer daemon itself upon bearer connection
status updates.

Scripts installed by users should go into the
/etc/ModemManager/connection.d directory.

Scripts installed by packages should go into the
/usr/lib/ModemManager/connection.d directory.

The name of the script will specify the order how it's run, so it's
suggested to name them with a numeric prefix, e.g. "99-something".

src/Makefile.am

@@ -294,6 +294,8 @@ ModemManager_CPPFLAGS = \
 	-DPLUGINDIR=\"$(pkglibdir)\" \
 	-DFCCUNLOCKDIRPACKAGE=\"${pkglibdir}/fcc-unlock.d\" \
 	-DFCCUNLOCKDIRUSER=\"${pkgsysconfdir}/fcc-unlock.d\" \
+	-DCONNECTIONDIRPACKAGE=\"${pkglibdir}/connection.d\" \
+	-DCONNECTIONDIRUSER=\"${pkgsysconfdir}/connection.d\" \
 	-DMM_COMPILATION \
 	$(NULL)
 
@@ -315,6 +317,8 @@ ModemManager_SOURCES = \
 	mm-auth-provider.c \
 	mm-dispatcher.h \
 	mm-dispatcher.c \
+	mm-dispatcher-connection.h \
+	mm-dispatcher-connection.c \
 	mm-dispatcher-fcc-unlock.h \
 	mm-dispatcher-fcc-unlock.c \
 	mm-filter.h \