Install calcurse-caldav by default

Add a new Makefile to build and install calcurse-caldav and include it
in the top-level build process.

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

contrib/caldav/Makefile.am

@@ -0,0 +1,13 @@
+AUTOMAKE_OPTIONS = foreign
+
+dist_bin_SCRIPTS = \
+	calcurse-caldav
+
+EXTRA_DIST = \
+	calcurse-caldav.py
+
+CLEANFILES = \
+	calcurse-caldav
+
+calcurse-caldav: calcurse-caldav.py
+	cp "$(srcdir)/$<" "$@"