move diff opening to scm and generalize usage

package.json

@@ -109,7 +109,7 @@
         "c9.ide.run.build": "#0598fff697",
         "c9.ide.run.debug.xdebug": "#9956689819",
         "c9.ide.save": "#4cda35bfdb",
-        "c9.ide.scm": "#9ab6e1b1c9",
+        "c9.ide.scm": "#6d333516cc",
         "c9.ide.terminal.monitor": "#1a4092ede2",
         "c9.ide.test": "#102942ae4e",
         "c9.ide.test.mocha": "#fc053b23d2",