Allow simple JSON configuration for site sessions

Different terminals need different hotkeys, but I want the kitty
configuration to be shared. Add a blanket json file to allow
creating more advanced configurations per site while keeping the
rest of the config common.

efx_site.default

@@ -0,0 +1,10 @@
+{ "sessions":
+    [
+        { "title": "System Shell",
+          "cmd": "/bin/bash --login"
+        },
+        { "title": "C Shell",
+          "cmd": "/bin/csh"
+        }
+    ]
+}