Moved finding of RSVG, Poppler-glib and GtkGl out into their own Find*.cmake modules to enable easier specialization.

CMakeModules/FindRSVG.cmake

@@ -0,0 +1,16 @@
+#use pkg-config to find various modues
+INCLUDE(FindPkgConfig OPTIONAL)
+
+IF(PKG_CONFIG_FOUND)
+
+    INCLUDE(FindPkgConfig)
+
+    PKG_CHECK_MODULES(RSVG librsvg-2.0)
+    PKG_CHECK_MODULES(CAIRO cairo)
+
+    IF (RSVG_FOUND AND NOT CAIRO_FOUND)
+       SET(RSVG_FOUND FALSE)
+    ENDIF()
+
+
+ENDIF()