Reworked LV2 plug-ing support.

This enables all platforms to use LV2 plugins in non-GUI mode.  There is
still some work to do, like subgroup handling and better scalepoint
handling.

src/configtemplate.h

@@ -123,6 +123,9 @@
 /* Define if the ogg vorbis decoding library is present */
 #undef USE_LIBVORBIS
 
+/* Define if the LV2 support is present */
+#undef USE_LV2
+
 /* Define if midi support should be enabled */
 #undef USE_MIDI